Preheat oven to 350 degrees F (175 degrees C). Grease an 8-inch square baking pan.
In a medium bowl, stir together 1 1/2 cups flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, cream together 1/3 cup butter and 3/4 cup sugar until light and fluffy. Beat in vanilla and egg. Gradually add the dry ingredients to the butter mixture alternately with the milk, stirring until just combined. Gently fold in blueberries.
In a small bowl, stir together 1/2 cup flour, brown sugar, 2 tablespoons butter, and cinnamon. Sprinkle the topping over the batter in the baking pan.
Bake for 45 to 50 minutes in the preheated oven, or until a toothpick inserted into the center of the cake comes out clean. Cool in the pan before serving.
Interesting Facts
Blueberry buckle is a classic American dessert.
It is made with a moist cake-like base and a crunchy streusel topping.
The topping is made with butter, flour, sugar, and cinnamon.