Preheat the oven to 425 degrees. Remove the pie crust from the fridge and let it warm up to room temperature. Unroll each crust and use a 4-inch round cookie cutter to cut out nine circles.
Carefully press each of the 4 inch circles into one of the muffin cups. The edge of the dough should hang slightly over the top of the cup.
Fill each cup with apple pie filling.
Combine the leftover dough scraps and roll the dough with a rolling pin on a lightly floured surface until it’s around 1/8 inch thick. Using a pizza cutter, slice the dough into small strips, about ¼-inch wide.
Use a 3-inch round cookie cutter to cut the strips into circles.
Remove every other strip from the circle and place the strips horizontally on top of the mini pie. Weave the remaining strips vertically through the horizontal strips to form a lattice pattern on top of the apples.
In a small bowl, beat the egg until smooth, then brush the egg wash over the top of each pie with a pastry brush.
Sprinkle sugar on top of each pie.
Bake the pies in the preheated oven for 25 to 30 minutes, until the crust is golden brown. Allow them to cool to room temperature before serving.
You can make this recipe easier by skipping the top crust, and making a crumb topping with some butter, flour, and brown sugar instead. (You can use the extra dough to make more pies.)
If you don’t have a circle cookie cutter that’s the right size, you can use a large drinking glass instead.