Preheat oven to 375F degrees. Spray a 13x9-inch baking pan with baking spray and set aside.
In a large bowl (or in a food processor), combine brown sugar, flour and baking powder. Cut-in butter and egg using a pastry cutter, or pulsing using the food processor, until a crumbly dough forms.
Press half the dough into prepared pan to form the crust. Reserve the remaining dough for the topping.
In a separate bowl, whisk together sugar and cornstarch. Add blueberries and vanilla and gently mix until combined. Sprinkle blueberry mixture over the crust in a even layer. Then sprinkle remaining dough over the blueberry mixture to form a crumbly topping.
Bake for 45 minutes, or until golden brown. Cool completely before cutting into squares.
Recipe by Alida's Kitchen at https://www.alidaskitchen.com/2015/07/12/blueberry-crumb-bars-recipe/