Flour, for dusting
1 recipe Buttery Pie Dough
8 tbsp. unsalted butter
1⁄2 cup packed light brown sugar
1⁄2 cup granulated sugar, plus 1 tbsp. for sprinkling
3 tbsp. cornstarch
1 tbsp. ground cinnamon
15 soft caramel cubes
8 tart apples, such as Granny Smith, peeled, cored, and thinly sliced
1 egg, lightly beaten with 1 tbsp. water
On a lightly floured surface, roll 1 disk of dough into a 12" round. Fit into a 9" pie plate. Trim edges, leaving 1" dough overhanging edge of plate; chill 30 minutes.
Melt butter in a 1-qt. saucepan over medium heat. Stir in brown sugar, 1⁄2 cup granulated sugar, cornstarch, cinnamon, and caramels; cook, stirring occasionally, until sugars are dissolved and sauce is slightly thick, 5–7 minutes.
Heat oven to 400°. Arrange apples over dough. Pour sauce evenly over apples. Roll remaining disk of dough into a 12" round and place over top of pie. Pinch top and bottom edges together and fold under; crimp edges. Brush with egg mixture; sprinkle with 1 tbsp. sugar. Cut three 1"-long slits in top of pie. Bake until crust is golden brown and filling is bubbling, about 1 hour. Let cool completely before serving.