A “buckle” dessert is similar to a coffee cake, made with fruit (most often blueberry, but also blackberry, raspberry, and peach) and with a topping that “buckles” when it’s baked. Both blueberry buckle and peach buckle are popular in Texas.
 
The origin of “buckle” is unknown, but it possibly originated in New England. “Blueberry buckle” is cited in print from at least 1935.
 
 
Cooks.com
BLUEBERRY, BLACKBERRY, OR RASPBERRY BUCKLE  
2 c. flour
1/2 c. butter
1 c. milk
4 tsp. baking powder
2 c. sugar
4 c. berries
 
Cream butter and 1 cup sugar. Add dry ingredients and milk alternately. Mix berries and remaining sugar, and pour on top of cake batter. Bake in a 9x13 inch pan. When cooked, berries will be on bottom. Heat oven to 375 degrees, bake for about 40 minutes. Grease the pan. If using frozen berries, heat them first.
 
(Dictionary of American Regional English)
buckle n
A type of coffee cake, usu made with blueberries.
1959 Masterton Blueberry Hill Cookbook 271 VT, Blueberry buckle. This one does as well for breakfast as for dessert. Serve warm with cream…Toss the fresh blueberries in a little flour; then add them [to the batter]. Spread the batter in a greased and floured 9-inch square pan. Topping..sprinkle over batter. Bake.
1979 Flagg Cape Cod Cooking 124, Blueberry buckle...Blend butter and sugar, add egg and beat well. Stir in the milk. Sift flour, baking powder and salt together and stir into liquid mixture. Add the blueberries. Spread in a well buttered 9” square pan. Sprinkle with topping…Bake.
1983 Better Homes & Gardens July 89, Blueberry Buckle—A buckle is a dessert that features a cakelike topping baked with fruit..2 1/2 cups fresh or frozen unsweetened blackberries or blueberries.
1983 DARE File swMI, We grew up eating blueberry buckle; usually we picked the berries ourselves.
   
19 July 1935, Hammond (IN) Times, pg. 11, col. 3:
Something New—
Blueberry Buckle
1/4 cup shortening.
1/2 cup sugar.
1 egg.
1 cup flour.
1 1/2 teaspoons baking powder.
Few grains salt.
1-3 cup milk.
1 pint blueberries.
1/2 cup sugar.
1-3 cup flour.
1/2 teaspoon cinnamon.
1/4 cup butter.

Cream shortening, add sugar, and cream thoroughly. Add egg and mix well. Mix and sift the 1 cup flour, baking powder and salt; add alternatively with the milk to first mixture. Pour into a greased 8-inch square pan. Spread blueberries on the cake mixture.
 
Mix thoroughly the sugar, 1-3 cup flour and cinnamon; rub in the butter with finger tips.
 
Sprinkle this mixture over the berries. Bake in a moderate oven (375 deg. F.) 45 minutes. Serves 6 to 8.
—By Beulah V. Gillaspie in McCall’s Magazine, August.
 
5 October 1978, Lake Park (Iowa) News, pg. 3, col. 1:
PEACH BUCKLE
1 cup flour
1/2 cup sugar
1 teaspoon baking powder
1/4 teaspoon salt
1/2 cup soft butter
2 eggs
1 can peach pie filling
2 tablespoons sugar
1/2 teaspoon cinnamon
Mix the first six ingredients as you would for a cake batter and beat 2 minutes. Pour into a buttered 9” x 9” square pan. Spoon the peach filling evenly over the batter. Sprinkle the sugar and cinnamon over all. Bake 45 to 50 minutes at 350 degrees. Good served warm with half and half or ice cream.
 
Dallas (TX) Observer—Best of Dallas 2001
Best Dessert
Blueberry Buckle, York St.
6047 Lewis St., 214-826-0968
It’s gooey, buttery, crunchy, tangy and warm. It’s all of the delicious things your mother used to do to baked dessert that no professional can duplicate. And it feels so much better going down than that other buckle mother used to dish out.
     
New York (NY) Times
In Dallas, a Taste (and a Sweet) for Every Palate
By MARK BITTMAN
Published: March 3, 2002
(...)
York Street
(...)
It was here that I began to believe Dallas had something unusual going in the dessert department. Blueberry buckle with cream was crunchy and cakey at once; pot au crème seemed a combination of fudge, mousse and chocolate chips; pecan pie was perfect.
 
Google Books 
America’s Best Kitchens—Southwestern Edition
by Cathy Leslie
Published by Lulu.com
2005
Pg. xv:
PEACH BUCKLE…TX-4  
 
18 August 2006, Dallas (TX) Morning News:
Select one or two of those to top a hot pastry like Texas peach buckle or chocolate brioche pudding. Add a bowl of fresh fruit, such as figs or apricots.
   
Forecast Earth
Get the Blues. You’ll Love ‘em.
Posted on June 17, 2008 at 9:32 am ET
Jay Weinstein, Forecast Earth Food Correspondent
(...)
Blueberry “buckle” is a fruity, cakey dessert named for the way the top scrunches up when it’s baked. I learned it from New England chef Jasper White, who was way ahead of his time in talking with his cooks about threats to fisheries and agriculture back before they were the urgent state they’re in today. He always pointed out that dishes should be made when their key ingredients are in season. At the restaurant, we started making this blueberry dessert in June, and ran it on the menu until blueberries went out of season later in the summer.
 
Blueberry Buckle
2 cups flour, divided use
1 ½ cups sugar, divided use
¼ teaspoon cinnamon
Pinch nutmeg
¾ teaspoon salt, divided use
8 Tablespoons butter, divided use
2 teaspoons baking powder
1 large egg
2 teaspoons vanilla extract
⅓ cup milk
2 ½ pints fresh blueberries (...)
 
Central Market, Summer 2008 (Dallas and Plano, TX)
SAT., JULY 19, 6:30 – 9 PM
COUPLES NIGHT OUT:TEXAS LOCAL-MOTION
CM Cooking School Staff
Eating locally, a movement being embraced across America, benefits the environment, thelocal economy and from a cook’s perspective, brings freshness and flavor to the plate. Learn the techniques necessary to produce this “Texas-Style Dinner” that celebrates our farmers, growers and producers whose ingredients areutilized in this bountiful meal: Paula’s Stacked Mozzarella & Tomato Salad; Herbed Bison Tenderloin with Red Wine Jus; Caramelized 1015 Onion & Texas Mushroom Bread Pudding; Farm Fresh Texas Vegetable Medley; and East Texas Blueberry & Peach Buckle with Homemade Vanilla Ice Cream. $120 per couple