Use mini muffin tins to make easy and delicious single-serve apple pies. Yield will vary depending on the size of the wells of your mini muffin tins (this sometimes varies by manufacturer). Yield and instructions below are based on a standard tin.
Combine apples, 1 cup raspberries, light brown sugar, 2 tablespoons granulated sugar, cinnamon, and salt in a large pot. Cover and cook over medium-low heat, stirring occasionally, until apples are soft but still retain their shape, 15 minutes. Stir in cornstarch mixture and continue cooking, uncovered, until juices are thickened and clear, 3-5 minutes. Cool to room temperature. Cut remaining 1/2 cup raspberries into halves and gently stir into the filling.
Make the topping for the pies by stirring together flour, 6 tablespoons granulated sugar, a pinch of kosher salt, and 3 tablespoons melted butter until crumbly. Set aside. Brush the wells and tops of the mini muffin tins with melted butter. Roll pie dough to 1/8-inch thick and use a 2-3/4 inch biscuit cutter to cut dough into rounds. Fit dough into the wells of the muffin tins and refrigerate 30 minutes.
Preheat oven to 400°F. Fill each well almost to the top with the apple mixture and top with a few pinches of crumble. Place tins on baking sheets to catch any filling that might bubble over in the oven. Bake 20 minutes, rotate pans, and continue baking 10 minutes, until crust is light golden brown (loosely cover with foil if crumble is browning too quickly). Remove from oven and let stand 5 minutes. Use two forks to gently lift each pie from the tins and transfer to wire racks to cool before serving.