Step 1

Preheat oven to 375 degrees F (190 degrees C). Grease a 9x13-inch baking pan.

Step 2

Prepare buckle: beat sugar and butter in a bowl using an electric mixer until creamy and smooth. Beat in eggs. Whisk flour, baking powder, and salt together in a separate bowl. Stir flour mixture into creamed butter mixture, alternating with milk, until batter is just combined; fold in blueberries. Pour batter into the prepared pan.

Step 3

Prepare topping: combine sugar, flour, and cinnamon together in a bowl. Cut in cold butter using a pastry blender or 2 knives until topping is crumbly. Sprinkle topping over batter.

Step 4

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 40 to 45 minutes. Cool buckle on a wire rack.