The comal (or comalli) is a flat dish or griddle that is popularly used for making tortillas and other foods in Mexican and Tex-Mex cuisines. Comal County in Texas is named after this flat dish. “Comal” (or “comalli”) is cited in print from at least the early 1800s.
     
     
Wikipedia: Comal (cookware)
A comal is a griddle or grill typically used for cooking foods based on a tortilla, including quesadillas, a folded tortilla filled with cheese and/or meat heated on the comal.
 
The history of such cooking methods dates back to the Pre-Columbian era when corn was ground by stone, made into tortillas, then filled with whatever was available and heated over an open fire.
 
More recently the comal has found its way into the modern kitchen as a part of the stove top.
 
The comal is now generally a black (tempered) heavy cast iron flat round griddle pan with a handle with a hole in it for hanging, and approximately 11 1/2 inches in diameter. The comals can be found in standard chain department stores such as Target, et al., or specialty gourmet cooking shops, or online. In many Hispanic cultures, the comal is handed down from grandmother to mother to daughter, the idea being that a comal tempered over many years of usage will heat faster, and cook cleaner. Also, culturally, it is said that having eaten food cooked on a comal over your lifetime, a person will crave food cooked by that method, as it imparts a small amount of the mineral iron into your daily diet.
 
Handbook of Texas Online
COMAL COUNTY. Comal County (L-15) is located in south central Texas on the divide between the Blackland Prairies and the Balcones Escarpment.qv Its largest city and county seat, New Braunfels, is twenty-nine miles northeast of San Antonio and forty-five miles southwest of Austin. The county’s center lies at 29°48’ north latitude and 98°17’ west longitude. The county comprises 555 square miles of prairie and Hill Country terrain. The eastern quarter, below the Balcones Escarpment, is gently rolling grass and crop land ranging in elevation from 600 to 750 feet above sea level. The Blackland Prairie soil of this section is loam with clay subsoils and is well suited for cultivation. The elevation of the northwestern three-quarters of the county ranges from 750 to roughly 1,500 feet above sea level. The loam in this section varies from shallow to deep and has proved better suited for grazing than for cultivation. The Hill Country terrain supports more timber-live oak, mesquite, and Ashe juniper-and fewer grasses than the prairies of eastern Comal County. Indigenous wildlife includes deer, doves, rabbits, turkeys, squirrels, ringtail cats, skunks, bobcats, and coyotes. Ranchers have also introduced several exotics into the area, including axis deer, sika deer, and Barbados sheep. The annual precipitation averages 33.19 inches, and average temperatures range from a low of 40° F in January to a high of 96° in July; the growing season lasts 265 days. Mineral resources include limestone, sand, and gravel; these have become the basis of a construction-materials industry in the county.
 
The Guadalupe River and, since 1964, Canyon Lakeqv drain the central hills and valleys of the county. Cibolo Creek, which empties into the San Antonio River, forms the southwestern boundary of the county and is the primary drainage channel for that area. Numerous streams north and east of Canyon Lake flow north into the Blanco River in Hays County. The Balcones Fault zone of the Edwards Aquifer is the primary source of groundwater in Comal County.
 
Spanish explorers were familiar with the Comal Springsqv area but evinced little interest in settling the region. After the expedition of Domingo Terán de los Ríosqv of 1691, the Old San Antonio Roadqv crossed the Guadalupe River near the future site of New Braunfels. Subsequent French and Spanish expeditions, including those of the Marqués de Aguayo and Louis Juchereau de St. Denis, commonly passed through what later became southeastern Comal County. In 1756 Comal Springs became the site of the short-lived Nuestra Senora de Guadalupe Mission, but, rather than fortify the mission against anticipated Comanche depredations, Spanish authorities closed it in 1758. Nearly a century passed before settlement became permanent, although a Mexican land grant of 1825 gave title of the area around the springs to Juan M. Veramendi. During the eighteenth century the springs and river (which had been called Las Fontanas and the Little Guadalupe respectively) took the name Comal, Spanish for “flat dish.” It is thought that the name was suggested to the Spanish by the numerous small islands in the river or by the shallow basin through which the river runs. 
 
Google Books
Present State of the Spanish Colonies
by William Walton, Jun.
Volume II
London: Longman, Hurst, Rees, Orme, and Brown
1810
Pg. 320:
Some dry it in the comalli or pan, in which they bake their bread of maize. 
 
Google Books
Annual Register,
Or a View of the History, Politics and Literature for the Year 1810
London; W. Otridge and Son
1812
Pg. 616:
Of maize they make their bread, which is totally different to the bread of Europe in taste, in appearance, and in its preparation. They put the grain to boil in water, with a little lime; when it becomes soft, they rub it in their hands to strip off the skin, then pound it in the metlatl, or stone in which they grind their maize; then they take out a little of the paste ,and stretching it by beating with both hands, they form the bread, after which they give it the last preparation in the comalli, which is a round, and rather hollow pan, about an inch thick, and fifteen inches in diameter. The form of the bread is round and flat, about eight inches in diameter, some less than a quarter of an inch in thickness, and some as thin as strong paper.
 
Google Books
Memoirs of the Mexican Revolution
by William Davis Robinson
Volume I
London: Lackington, Hughes, Harding, Mavor, & Lepard
1821
Pg. 163:
The bread consumed by the Mexicans generally, but particularly by the country people, is made of Indian corn, and by a process unknown elsewhere. The quantity of corn, necessary for the daily consumption of the family, is put to steep, over night, in a large earthen vessel, in hot water, mixed with lime. This softens the husk, and in the morning it is ready for the next step in the process; but the taste of the corn, and the greatest part of its substance, is extracted by this preparation. It is then ground up, with much labour, between two flat stones, called by the Indians a metate; and afterwards formed, by beating it between the hands, into cakes, about eight or ten inches in diameter, and about one-sixteenth of an inch in thickness. They are then placed on an earthen heater, or griddle (comal), and baked. These caked they call tortillas. The preparation of them is entirely performed by women; and, if the family be large, it requires four or five to perform this duty. The art of making tortillas is considered of great importance by the natives; and its excellency consists in grinding the grain till it becomes white, making the cakes thin, and, above all, in keeping the table supplied with a succession of hot ones during the meals.
 
Google Books
The History of Ancient Mexico
by Thomas F. Gordon
Volume I
Philadelphia, PA: Printed for and Published by the Author
1832
Pg. 318:
Every house was supplied with the metlatl, and comalli. The former is the stone mortar, in which the women grind their maize and cacao. This instrument is still extremely common in all New Spain, and over the greatest part of America. The Europeans have also adopted it, and in Italy and elsewhere the chocolate makers use it to grind the (Pg. 319—ed.) cacao. The comalli, as much used as the metlatl, is a round and hollow pan, about one inch deep, and fifteen in diameter.
 
Google Books
Incidents of Travel in Central America, Chiapas, and Yucatan
by John L. Stephens
Volume I
Tenth Edition
London: John Murray
1842
Pg. 109:
The furniture consisted of a stone roller for mashing corn, and a comal or earthen griddle for baking tortillas;...
 
Google Books
Life in Mexico During a Residence of Two Years in that Country
by Mme. Calderon de la Barza
Volume II
Boston, MA: Charles C. Little and James Brown
1843
Pg. 361:
We staid some hours on the island, and went into some of the huts where the women were baking tortillas, one Indian custom at least, which has descended to these days without variation. They first cook the grain in water with a little lime, and when it is soft peel off the skin—then grind it on a large block of stone, the metate, or, as the Indians (who know best) call it, the metatl. For the purpose of grinding it, they use a sort of stone roller, with which it is crushed, and rolled into a bowl placed below the stone. They then take some of this paste, and clap it between their hands, till they form it into light round cakes, which are afterwards toasted on a smooth plate, called the comalli, (comal they call it in Mexico) and which ought to be eaten as hot as possible.
 
Google Books
The Progress of America, from the Discovery by Columbus to the Year 1846
by John Macgregor
Volume 1, Part 2
London: Whittaker and Co.
1847
Pg. 793:
TORTILLAS.—On entering another house, he found “the whole family engaged in making tortillas. This is the bread of Central and of all Spanish America, and the only species to be found except in the principal towns. At one end of the cucinera was an elevation, on which stood a comal, or griddle, resting on three stones, with a fire blazing under it., The daughter-in-law had before her an earthen vessel containing Indian corn soaked in lime-water to remove the husk, and placing a handful on an oblong stone, curving inward, mashed it with a stone roller into a thick paste. The girls took it as it was mashed, and patting it with their hands into flat cakes, laid them on the griddle to bake. This is repeated for every meal, and a great part of the business of the women consists in making tortillas.
 
Google Books
Incident of Travel in Yucatan
by John Lloyd Stephens
New York, NY: Harper & Brothers
1848
Pg. 127:
The hut of which we thus became the sudden and involuntary masters was furnished with three stones for a fireplace, a wooden horse for kneading maize upon, a comal for baking tortillas, an earthen olla, or pot, for cooking, three of four waccals, or gourds, for drinking-cups, and two small Indian hammocks, which also were demanded and given up.
 
Google Books
The White Chief:
A Legend of Northern Mexico
by Captain Mayne Reid
Volume I
London: David Bogue
1855
Pg. 237:
Tortillas are only eaten warm—that is, are fit only for eating when warm—or fresh from the “comal.” They are, therefore, to be baked immediately before the meal commences, or during its continuance.
 
Rosita set the olla on one side, and placed the comal over the coals. Another olla, which contained maize—already boiled soft—was brought forward, and placed beside the “metate,” or tortilla-stone; and then, by the help of an oblong roller—also of stone—a portion of the boiled maize was soon reduced to snow-white paste. The metate and roller were now laid aside; and the pretty, rose-coloured fingers of Rosita were thrust into the (Pg. 238—ed.) paste. The proper quantity for a “tortilla” was taken up, first formed into a round ball, and then clapped out between the palms until it was only a wafer’s thickness. Nothing remained but to fling it on the hot surface of the comal, let it lie but for an instant, then turn it, and in a moment more it was ready for eating.
 
Google Books
Notes on the Manufacture of Pottery Among Savage Races
by Charles Fred Hartt
Rio de Janeiro: Printed and published at the office of the South American Mail
1873
Pg. 55:
The class of pottery used by the poorer people comprises the comal (flat plates to bake tortillas on), cajetes or small plates (saucers) for certain dishes etc. 
     
Live Search Books
On the Xinca Indians of Guatemala
by Daniel Garrison Brinton
(Read before the American Philosophical Society, October 17, 1884.)
Pg. 6:
Plate, in the original, comal, Nahuatl comalli, a shallow earthen dish used to prepare tortillas. 
 
Live Search Books
Dialect Notes
published by the American Dialect Society
Volume I
Norwood, MA: J. S. Cushing & Co.
1896
Pg. 189 (Spanish and Mexican Words Used in Texas):
comal: a slightly hollow utensil of stone or earthenware on which tortillas are cooked or baked. Name of a river and a county in Texas. From Mexican comalli (S.).
 
Google Books
A New Dictionary of Americanisms
by Sylvia Clapin
L. Weiss & Co.
1902
Pg. 128:
Comal (Mex. ... of stone or earthenware on which ” tortillas” are cooked or baked.

The Tex-Mex Cookbook
by Robb Walsh
New York, NY: Broadway Books
2004
Pg. 11:
COMAL
A flat cast-iron pan without sides, the comal is traditionally used to cook tortillas. You can sustitute a cast-iron skillet. Roasting tomatoes, peppers, or garlic in a comal is a typical step in making salsa. In this case, “roasting” means placing the ingredient in a dry, ungreased comal and heating it until lightly charred.