In a food processor, combine gluten-free all-purpose baking flour, salt, granulated sugar, and cold cubed unsalted butter. Pulse until the mixture resembles coarse crumbs. Gradually drizzle in ice water, pulsing just until a smooth dough forms. Shape it into a disk and wrap in plastic wrap.

Place the wrapped dough in the refrigerator and let it chill for at least 30 minutes.

While the dough chills, peel and finely dice your apples. In a mixing bowl, combine the diced apples with light brown sugar, ground cinnamon, nutmeg, and gluten-free all-purpose flour. Toss well.

Preheat your oven to 425°F (220°C) and prepare your muffin tin by greasing it lightly.

Once chilled, remove the dough and roll it out to about 1/8 to 1/4 inch thickness. Cut out circles of dough using a 4-inch cookie cutter.

Press the dough circles into the greased muffin tins. Spoon the apple filling into each crust and brush the edges with the beaten egg.

Bake the Mini Apple Pies for 20–24 minutes, or until golden brown and bubbly. Let cool in the tin for about 10 minutes before transferring to a wire rack.