Preheat oven to 375 degrees Fahrenheit. Line a 13×9-inch baking dish with parchment paper (for lifting the bars out) or lightly grease with cooking spray.

In the bowl of a stand mixer, stir together the flour, sugar, baking powder, and salt. Add the butter one Tablespoon at a time and mix with the paddle attachment until the ingredients resemble fine crumbs. Add the egg and mix until incorporated. (Note: Crumbs will start to clump together the longer it is mixed. Don’t let it ball up though; keep it slightly crumbly.)

Press 1/2 to 2/3 of the mixture onto the bottom of the prepared baking dish. Bake at 375˚F for 10-12 minutes or until the crust is matte (not shiny/wet) and starting to lightly brown.

Dollop the blueberry pie filling onto the partially baked crust, and spread evenly with a spatula.

Crumble the remaining crust evenly over the top of the blueberry filling. (Squeeze crumbs together in hands for bigger chunks.) Bake at 375˚F for an additional 25-30 minutes until the top is lightly brown and the filling bubbles in the center. Remove from oven and place on a wire rack to cool completely.

Once bars are cool, mix together 1 cup powdered sugar, 1 tsp vanilla extract and 1 Tbsp milk. Check consistency and add up to one more Tablespoon of milk, if desired. Drizzle over cool bars and allow glaze to set. Use parchment paper to lift bars out of pan. Cut and serve.