Make a batch of All-Purpose Flakey Pie Crust.
Roll out pie crust and cut into 3-inch squares. In the center of each square, place a spoonful of cranberry sauce (1-2 teaspoons). Fold the corners of the dough in and pinch them firmly together. Carefully transfer to a parchment-lined baking sheet, spacing an inch or so apart. Freeze for 30 minutes.
Brush tartlets with milk and sprinkle with sanding sugar. Bake at 400 degrees until golden, 30 to 35 minutes. Remove to cooling racks for at least 20 minutes until filling has cooled; serve warm.