Add the butter and sugar to a mixing bowl and using a hand mixer whip them together until smooth & creamy. Add the eggs and extract, mixing together again until evenly combined.
1 cup salted butter, 1 3/4 cups sugar, 1 tsp vanilla extract, 4 eggs
To another mixing bowl add the flour and baking powder then stir them together until evenly combined. Slowly add the flour mixture into the wet batter, mixing together until completely incorporated.
3 cups flour, 1 1/2 tsp baking powder
Spray a 9x13" baking dish with nonstick cooking spray. Set aside 1 1/2 cups of batter then transfer the rest to the prepared baking dish and spread it out in an even layer.
Spread the blueberry pie filling evenly out overtop, then drop teaspoon sized dollops of the reserved dough evenly out overtop.
2 3/4 cups blueberry pie filling
Bake at 350° for 35 minutes, just until the batter's set. Carefully remove the hot dish from the oven and let it cool for 40 minutes.
Mix the remaining ingredients together until a glaze is formed, thinning with 1-2 tablespoons of milk as needed. Drizzle the glaze over the dish.
1 1/2 cups powdered sugar, 1 tsp vanilla extract, 1-2 tbsp milk
Slice, serve, and enjoy!