Preheat your oven to 375°F (190°C).

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, light brown sugar, baking powder, and baking soda until smooth.

Using a pastry cutter, work in the cold butter until the mixture resembles small crumbs.

Add the egg, mixing until fully incorporated into the dough.

Press about ¾ of the dough into the bottom of a 9x13 inch baking dish to form your crust. Save the remaining dough for topping.

In another bowl, mix thawed blueberries with lemon juice, vanilla extract, and cornstarch until well-coated.

Pour the blueberry mixture evenly over the crust. Then, sprinkle the reserved crumb mixture on top.

Bake for about 40 minutes or until the topping is golden brown.

Let it cool on the counter for about 20 minutes before slicing. Serve and enjoy!