Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.

In a large mixing bowl, combine 2 cups of all-purpose flour, 1 cup of granulated sugar, 1 teaspoon of baking powder, ½ teaspoon of salt, and 1 teaspoon of ground cinnamon; whisk until mixed.

Cut in ½ cup of chilled, cubed unsalted butter and 1 large egg into the flour mixture until crumbly.

Press half of the crumbled dough mixture into the bottom of the prepared baking dish to form a crust.

In another bowl, combine 4 cups of diced mixed apples, ½ cup of light brown sugar, 2 tablespoons of cornstarch, 1 tablespoon of lemon juice, and 1 teaspoon of vanilla extract; toss until coated.

Spread the apple mixture evenly over the crust in the baking dish.

Sprinkle the remaining crumb mixture over the apple filling and press gently to adhere.

Bake for 40 to 45 minutes, until golden brown and the apple juices are bubbling.

Let cool completely in the pan before slicing into squares.