Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x9-inch baking pan.
Mix 1 1/4 cups flour, 1/2 cup white sugar, baking powder, baking soda, and salt together in a bowl using a fork. Stir 1/2 cup butter, milk, egg, and vanilla extract into flour mixture until evenly combined. Pour batter into prepared pan.
Combine 1/2 cup flour, 1/4 cup white sugar, and 3 tablespoons butter in a bowl using a fork until mixture resembles crumbs; sprinkle half the crumb mixture over the batter.
Stir blueberry pie filling and lemon extract together in a bowl; spread over crumb topping. Sprinkle blueberries over pie filling; top with remaining crumb topping.
Bake in the preheated oven until cake is golden brown, about 1 hour.
