01 -
Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper.
02 -
In a bowl, whisk together flour, granulated sugar, brown sugar, baking powder, and salt. Cut in cold butter until mixture resembles coarse crumbs. Add egg and vanilla extract, mixing until a soft dough forms.
03 -
Press about two-thirds of the dough firmly into the bottom of the prepared pan to create an even crust layer.
04 -
In a large bowl, toss the sliced apples with granulated sugar, brown sugar, cornstarch, cinnamon, nutmeg, lemon juice, and vanilla extract until apples are evenly coated.
05 -
Spread the apple mixture evenly over the crust base. Crumble the remaining dough over the apples to create a topping.
06 -
Bake in the preheated oven for 45–50 minutes until the topping is golden brown and the filling is bubbling at the edges.
07 -
Allow to cool at room temperature for at least 45 minutes to ensure filling sets.
08 -
Whisk powdered sugar, milk, and vanilla extract until smooth. Drizzle glaze evenly over cooled bars.
09 -
Cut into bakery-style squares and serve.