Preheat your oven to 350°F (175°C). In a stand mixer, combine all-purpose flour, granulated sugar, and chilled unsalted butter. Blend on low speed until the mixture resembles coarse crumbs, about 2–3 minutes. Press two-thirds of the mixture evenly into a parchment-lined 9x13-inch baking pan, creating a solid base. Reserve the remaining mixture for the topping.

In a large skillet over medium heat, melt a tablespoon of butter and add the sliced apples, brown sugar, lemon juice, and cinnamon. Sauté for about 10 minutes, stirring occasionally until the apples are just tender, but still hold their shape. Remove from heat, allowing the mixture to cool slightly before spreading it over the crust in the baking pan.

Once the apple filling is evenly distributed over the crust, sprinkle the reserved crumb mixture on top. Ensure that the topping covers the apples but allows some visibility of the filling beneath.

Place the assembled baking pan in the preheated oven. Bake for 45–55 minutes, or until the top is golden brown and the filling is bubbly around the edges.

After baking, remove the pan from the oven and allow it to cool at room temperature for at least 30 minutes. Once cooled, slice into squares using a sharp knife, and serve warm.