To prepare the shortbread crust, preheat the oven to 350°F and line an 8x8-inch baking pan with parchment paper.

Beat sugar, light brown sugar, and butter until it becomes light and fluffy, using medium speed for approximately 2-3 minutes.

Add vanilla and beat until well combined, then fold in flour and salt, continuing to mix at low speed until you achieve crumbly dough. Press this dough into the bottom of the prepared pan and bake for 12-14 minutes.

For the apple filling, begin by peeling and thinly slicing the apples. Combine them with flour, light brown sugar, cinnamon, and nutmeg in a medium dish.

Once the shortbread layer is ready, remove it from the oven while keeping the temperature at 350°F. Spread the apples over the shortbread layer.

To prepare the crisp topping, place all the necessary ingredients in a dish and cut in the butter until it becomes crumbly using a pastry cutter.

Spread the crisp topping over the apples and bake for approximately 45 minutes, or until the topping turns golden.

Allow it to cool in the pan, then remove it and cut it into bars.