Tortilla soup (sopa de tortilla in Spanish) contains strips of corn tortillas added to various other soup ingredients. The dish appears to have originated in Mexico City and can be found in the books Nuevo y Sencillo Arte de Cocina (1836) and Diccionario de Cocina (1845).
 
“‘Sopa de Tortilla’ (soup, made with the Indian corn tortilla, and flavoured)” was printed in the book Mexico as I Saw It (1901) by Ethel Brilliana Harley Tweedie. Recipes for tortilla soup were printed in the book Castelar Crèche Cook Book (1922) and in the newspapers the Beaumont (TX) Enterprise on November 21, 1925; the New York (NY) Herald Tribune on June 21, 1942; and The Oregon Statesman (Salem, OR) on July 22, 1959. The dish became common in Mexican-American restaurants by the 1960s and 1970s.
 
“To be really authentic, the soup should have only a little white onion, raw not cooked, blended with roasted tomato,” Mexican cookbook author Diana Kennedy told the Los Angeles (CA) Times on November 30, 2005. Modern versions of tortilla soup have a tomato base with garlic, onion, chile de árbol and epazote.
 
Tortilla soup is sometimes called “Aztec (Tortilla) Soup” (Sopa Azteca).
 
   
Wikipedia: Tortilla soup
Tortilla soup (Spanish: sopa de tortilla) is a traditional Mexican soup made of fried corn tortilla pieces, submerged into a broth of tomato, garlic, onion, and chile de árbol and epazote. It is served with pieces of pasilla chiles, chicharrón, avocado, fresh cheese cubes and sour cream. Although this exact origin of tortilla soup is unknown, it is known that it comes from the Mexico City area in Mexico. Traditional tortilla soup is made with chicken broth combined with roasted tomatoes, onion, garlic, chiles and tortillas, cut into strips and fried. There are some variations, for example the broth being made with a thickened tomato base and ground tortillas or a bean soup enriched with crunchy strips of fried tortillas.
         
Google Books
Nuevo y sencillo arte de cocina, reposteria y refrescos, Volumes 1-2
By Antonia Carrillo
Mexico: Imprenta de Santiago Perez
1836
Pg. 30:
38.—SOPA DE TORTILLA.
Se freiran en mantequilla unos ajos, y ya dorados, se sacaran y se freira la tortilla cortada en tiras angostitas como tallarin, y con sal, y asi que este frita que suene como seca, se le echara, el caldo ya sazonado, yerba-beuna picada, y se dejara hervir, procurando que no quede ni muy reseca ni my caldosa.
(They will fry some garlic in butter, and when they are golden brown, remove the tortilla and cut it into angostitas strips such as tallarin, and with salt, and so that this fried that sounds like dry, it will be thrown, the broth already seasoned, yerba Beuna, chopped, and let boil, trying not to be too dry or too hot.—ed.)
 
Google Books
Diccionario de cocina: o el nuevo cocinero mexicano en forma de diccionario ...
By Mariano Galván Rivera
México: Imprenta de I. Cumplid
1845
Pg. 796:
SOPA DE TORTILLA. Envueltas las tortillas se rebanarán en ruedas muy delgadas, y se guardan para el dia siguiente, en que se pondrá al fuego una tortera con manteca, se frien en ella tres ó cuatro dientes de ajo picados, y en seguida las tiritas de tortilla; estando bien fritas, se echará caldo suficiente con unas hojas de epazote, y cuando haya consumido de modo que no quede seca, se servirá adornándola lo mismo que la de pan.
(Wrapped tortillas will be sliced ​​on very thin wheels, and saved for the next day, which will be put on the fire a tortera with butter, fried in it three or four cloves of garlic, and then the tortilla strips; when well fried, enough broth will be poured with epazote leaves, and when it has been consumed so that it does not remain dry, it will be served by decorating it as well as bread.—ed.)
   
Chronicling America
20 May 1893, El Fronterizo (Tucson, AZ), “Recetas Utiles,” pg. 4, col. 3:
SOPA DE TORTILLA AL VAPOR.—Se unta una cazuela con mamtequia y se le pone una capa de cuarteronos de tortilla frita y otra de recaudo frita y polvo de queso seco. Ensima se le ponen unas yemas de huevos cocidas y. molidas y unos trocitos de montequilla. Se cuece al vapor.
(TORTILLA SOAP WITH STEAM. - Spread a casserole with machete and put a layer of fried tortilla cuarteronos and another fried and dried cheese powder. Ensima is put some yolks of cooked eggs and. ground and a few pieces of montequilla. It is steamed.—ed.)
 
Google Books
Mexico as I Saw It
By Ethel Brilliana Harley Tweedie
London, UK: Hurst and Blackett, Limited
1901
Pg. 306:
The Mexican menu, composed by his wife, was representative of ht every-day fare of the country:
 
“‘Sopa de Tortilla’ (soup, made with the Indian corn tortilla, and flavoured).”
       
30 July 1910, Brownsville (TX) Daily Herald, pg. 5, col. 5:
RESTAURANT.
The Grand Hotel Libertad.
Matamoros, July 31, 1910.
(...)
Tortilla Soup
 
Mexican Cooking
Gebhardt Chili Powder Co.
San Antonio, Texas
1911
Pg. 32:
Sopa de Migas—Tortilla Soup…
 
Chronicling America
15 October 1915, Caldwell (ID) Tribune, “With the Housewife,” pg. 3, col. 3:
Sopa de tortilla, a thick gravy with corn cakes chopped small, makes a pleasing native soup that is entirely unlike any of our country.
 
Google Books
Castelar Crèche Cook Book
Los Angeles, CA: Times-Mirror Printing and Binding House
1922
Pg. 280:
TORTILLA SOUP
Cut the tortillas in equal sizes, put them in hot lard, but do not fry them. Place in a Pyrex dish a layer of tortillas, then cheese chopped finely, then chopped uncooked marrow out of a soup bone (which has been left 1 or 2 hours in water to be perfectly free of blood), some parsley very finely chopped, strips of green peeled chiles and a sauce made of tomatoes (take them out of can but without any water), salt, pepper and mashed onions and a bit of garlic. Put layers of all these things on top some cheese and marrow. Then fill the dish about 3/4 full of bouillon and let it boil to absorb the bouillon and remain dry.—Carlota L. Algara.
 
21 November 1925, Beaumont (TX) Enterprise, “Steaming Soups Return to Favor with Coming of Frost,” pg. 14, col. 2:
Tortilla Soup.
Take some tortillas and cut into small pieces; drop them in a frying pan where you have previous heated some lard. When slightly brown, add one button of garlic and onion chopped fine, one sliced red tomato (or five or six mashed green tomatoes), salt, pepper, one to one and one-half teaspoonfuls of Gebhardt’s Eagle powder and one-half teacupful of hot water; let boil for about ten minutes and then serve.
     
1 July 1934, San Antonio (TX) Express, pg. 1D, col. 2:
Among the many dishes for which tortillas are used I may mention principally the well known enchiladas, tacos, quesa dillas, chilaquilles, eggs country style or huevos rancheros, tortilla soup, and others … 
 
2 March 1937, Dallas (TX) Morning News, “Texas Independence Day Program to be Heard over NBC-WFAA Tuesday,” sec. 2, pg. 2, col. 2:
Mexican Recipes on Air.
Authentic Mexican recipes for tortilla soup, picadillo and frijoles refritos, will be given on the Modern Homemaking program at 10:45 a.m.
   
21 June 1942, New York (NY) Herald Tribune, “It’s Not All Tamales: Mexico cooks many foods to our liking—just try these recipes” by Margarol Goldsmith, This Week magazine sec., pg. 21, col.s 3-4:
Tortilla Soup
6 canned tortillas
2 tablespoons butter
6 large spinach leaves, minced
2 cups meat stock
grated cheese
Cut the tortillas in thin strips and saute in butter until crisp and lightly browned. Bring soup stock to a boil, add spinach and sauteed tortillas and let simmer uncovered for 10 minutes. Serve at once with a generous sprinkling of grated cheese on each serving. Approximate yield: 4 portions.
 
22 July 1959, The Oregon Statesman (Salem, OR), “Frozen Foods Include Mexican Specials Also” by Maxine Buren, sec. 1, pg. 8, col. 4:
Dry Tortilla Soup
6 tortillas
1/2 cup oil
1 onion, minced
2 cups tomato puree
1 bay leaf
1 teaspoon oregano
Salt and pepper to taste
Grated cheese
6 hard cooked eggs
Cut tortillas into strips like macaroni. Fry in oil until crisp. Set aside to drain on brown paper. Fry minced onion in oil in which tortillas were cooked. Add tomato puree, season and cook for about half an hour. Butter a casserole, place tortillas in layers with sauce, grated cheese and round slices of hard cooked eggs. When all ingredients are used, with rounds of eggs on top cover with remaining sauce and bake in moderate oven (350 degrees) for about 30 minutes. This recipe serves six.
 
19 June 1964, New York (NY) Times, “Dining at the Fair” by Craig Claiborne, pg. 14, col. 2:
(Focolare restaurant, Mexican Pavilion, New York World’s Fair.—ed.)
One of the best-known of Mexican soups is made with crumbled tortillas in a rich broth and at the Focolare the tortilla soup ($1.20) is good but not exceptional. The broth seems a trifle mild when compared with those of some restaurants in Mexico and it seems to lack the characteristic flavor of chile.
   
23 November 1972, Deer Park (TX) Progress, “Comida Mejicana” by El Comilon, pg. 8A, cols. 5-6:
Sopa de Tortilla, tortilla soup.
   
As in all national dishes, there are many variations of the original which consisted of chicken or meat broth with crisp tortilla pieces floating in it. The “Cocinero” (chef) at the Montejo does one of the best I have found and here is the way I have watched him do it in his kitchen:
 
Cut 6 or 8 stale tortillas in narrow strips, less than 1/2 inch wide, and fry them in hot oil until lightly brown. Drain and keep warm.
 
Heat about a half gallon of chicken stock (or meat stock or canned consomme) with a finely chopped onion, carrot wheels, zucchini pieces and bite size celery sticks. Simmer until the vegetables are done but crisp. A few minutes before it is done, add half a cup of tomato puree.
 
Place the tortilla strips in the bottoms of the serving bowls, pour the soup over them and garnish with chopped, fresh cilantro (coriander). If you cannot find the fresh cilantro use fresh parsley and a touch of grated lemon rind…do not use dry coriander because the flavor is quite different. Serve grated cheese to add at the table.
   
16 February 1975, Dallas (TX) Morning News, “Tortilla Soup, Si! Dulce Tamale, No!” by Frank X. Tolbert, section A, pg. 35:
Truth is, not many cafes along the Tex-Mex border serve tortilla soup. Most of them go in for the stew called menudo, the basic ingredient of which is tripe.
   
Google Books
The Food of Texas:
Authentic Recipes from the Lone Star State
by Caroline Stuart
Tuttle Publishing
2000
Pg. 48:
TORTILLA SOUP
Dan Fearing, The Mansion on Turtle Creek, Dallas
Tortilla soup is a Southwestern classic, and probably the most popular soup in Texas. It’s basically chicken soup that has been glorified with tomatoes, interesting Mexican spices, herbs, and chile peppers. Fried tortilla strips garnish the soup along with avocado cubes and shredded cheese. It’s hearty enough to serve as a meal. If you’re not going to serve it right away, make the soup ahead of time and add the garnishes at the last minute.
       
Internet Movie Database
Plot summary for
Tortilla Soup (2001)
Retired Mexican-American chef Martin Naranjo shares an L.A. home with his three gorgeous, but single, adult daughters. Though he long ago lost his ability to taste, Martin still lives to cook incredibly lavish dinners for his loved ones and to serve them in a family-style ritual at traditional sit-down meals. Although the women humor their father’s old-fashioned ways, each of them is searching for fulfillment outside the family circle. College student Maribel is growing increasingly frustrated with the singles scene and wants a steady man; gorgeous career woman Carmen is fed up with her boyfriend and his wandering eye; meanwhile, eldest daughter Letitia, who has suppressed her own romantic longings, senses something missing in her life. Things take a turn for the romantic when Dad, a widower, meets a vivacious divorcee on the lookout for a mate and each of his daughters, in turn, finds someone. But they’ll all discover that the recipe for happiness may call for some unexpected ingredients. Written by Sujit R. Varma
 
The Tex-Mex Cookbook
by Robb Walsh
New York, NY: Broadway Books
2004
Pg. 137:
TORTILLA SOUP
The quick and easy Tex-Mex version of this Mexican classic is made with Rotel tomatoes and crispy tortilla chips. Made with abundant garlic, it’s not only delicious, it’s the cure for the common cold.
 
Los Angeles (CA) Times
A bowl of Mexican soup
The origins of tortilla soup may be a mystery, but its intriguing flavor has long made it a California favorite.
November 30, 2005 | Barbara Hansen | Times Staff Writer
(...)
Classic tortilla soup, the way you’d find it in Mexico City, is simply good chicken broth combined with roasted tomatoes, onion, garlic, chiles and tortillas, cut into strips and fried. It’s wonderfully satisfying, “a sort of soul food soup,” as Mexican cooking authority Diana Kennedy puts it.
 
In California, it’s often made with a tomato base thickened with ground tortillas, but there are variations, such as a bean soup enriched with crunchy strips of fried tortillas.
 
“To be really authentic, the soup should have only a little white onion, raw not cooked, blended with roasted tomato,” says Kennedy, speaking from her home near Zitacuaro in the state of Michoacan.
(...)
Oddly, no one knows where tortilla soup came from, not even Kennedy. “It’s certainly not all over Mexico,” she says. “It’s in the center, around Mexico City, the home of tortilla soup.”
 
Although Dan Strehl, culinary historian and translator of “Encarnacion’s Kitchen” (the 2003 cookbook drawn from Encarnacion Pinedo’s 1898 California cookbook “El Cocinero Espanol”) can’t pinpoint the arrival of tortilla soup in California, it had certainly made its way north by the mid 20th century. It appears in “Elena’s Famous Mexican and Spanish Recipes,” published in San Francisco in 1944. That recipe, by Elena Zelayeta, doyenne of Mexican cooking in California, is a simple combination of broth, tomato puree and tortilla strips, to which she added mint leaves.
   
Serious Eats (August 2012)
How to Make Real-Deal Tortilla Soup
J. KENJI LÓPEZ-ALT
(...)
According to a 2005 Los Angeles Times article, the exact origins of the dish have not actually been pinpointed, but it stemmed from somewhere in the Mexico City area, making its way to North to California and Texas by the mid 20th Century. By the 70’s and 80’s, it was a staple on Mexican and Tex-Mex menus all over the southern United States.
 
The most basic version starts as good chicken broth enriched with a puree of roasted tomatoes and onions, garnished with picked chicken meat and crunchy fried tortillas.
 
Saveur
MEXICAN TORTILLA SOUP (SOPA AZTECA)
BY FARIDEH SADEGHIN AUGUST 31, 2015
(...)
Crunchy tortilla chips were divided between bowls, and the pasilla chile- and tomato-based broth was ladled over the top. Topped with avocado, cheese, and crema, this dish was perfection.
(...)
Ingredients
1 large pasilla chile
1 (15-oz.) can diced tomatoes
2 tbsp. canola oil
3 cloves garlic, peeled
1 medium white onion, roughly chopped
8 cups chicken stock
1 epazote or cilantro sprig (optional)
1 1⁄2 lb. boneless, skinless chicken breast, cut into 1⁄2-inch pieces
Kosher salt and freshly ground black pepper
6 oz. shredded Monterey Jack cheese
1-2 avocados, diced
Crema or sour cream, for serving
Lime wedges, for serving
Tortilla chips (about 4 cups), crushed, for serving