Preheat your oven to 350°F and line a large baking sheet with parchment paper.
Lightly flour your work surface and roll out the pie crusts with a rolling pin until they’re about ⅛-inch thick. Use a 4½-inch biscuit cutter or the rim of a wide glass to cut out 12 circles of dough.
Arrange the dough rounds on the prepared baking sheet, leaving a little space between each one.
Spoon small portions of mashed potatoes, stuffing, turkey, and cranberry sauce onto one half of each dough circle, keeping the edges clear for sealing.
Fold the empty side of the dough over the filling to form a half-moon shape. Press the edges together, then seal them by crimping with the tines of a fork.
In a small bowl, whisk the egg with the milk. Brush this mixture over the tops of the hand pies to help them bake up golden and shiny.
Use a sharp knife to cut three small slits in the top of each pie to allow steam to escape while baking.
Bake for about 30 minutes, or until the crusts are crisp and golden brown.
Serve warm with leftover gravy and extra cranberry sauce for dipping.