• Position rack in the lower third of the oven, and preheat oven to 375°. Have ready a greased, 9x13" baking dish.

For the Crust:

• Add the flour, sugar, salt, and baking powder to the bowl of a food processor fitted with a paddle attachment. Pulse to mix. If you do not have a food processor, use a large mixing bowl and a whisk. 
• Add the cold, cubed butter and shortening and pulse until the mixture resembles small peas speckled throughout the dry ingredients. Or, you could use a pastry cutter to cut in the fats. 
• Add the egg and vanilla, and pulse combine. If you're not using a food processor, stir with a wooden spoon until evenly incorporated. Set aside until ready to use.

For the Blueberry Filling:

• In a large mixing bowl, combine blueberries, sugar, cornstarch, lemon zest, lemon juice, and salt. Stir to combine.
• Add about ⅔'s of the dough to the bottom of the greased casserole dish. Gently use your hands to pat the dough out evenly across the dish. Pour the blueberry filling evenly across the dough, and crumble the dough that remains over the top.
• Bake for 45 minutes, or until the crust is golden-brown. Place on a wire rack and allow to cool 15 minutes before cutting. Serve and enjoy.