Place 1 disk of dough onto a floured work surface. Working from the center out, roll the dough out to a circle about 12 to 14 inches in diameter.
Use a stamp (I used a rectangular glass container that was 4 1/2 inches by 3 1/2 inches) to stamp out the dough. Gather the scraps of dough, re-roll them, and repeat until the dough is gone (you should get about 12 circles from each disk of dough for a total of 24 circles from this recipe). You can chill the dough scraps at any point if it becomes too difficult to re-roll them out, or sprinkle on a little flour.
Place 1 1/2 tablespoons of apple filling in the center of each piece of dough. Leave a rim of about 1/4 inch around the outside so you can seal the pies.
Lightly wet your finger with water and run it on the dough along the outside of the apple filling to help the other piece of dough stick on top. Place another piece of dough on top. Continue this way until all the pies are formed. You should get 24 pies total.
Use a thin metal spatula to lift up each pie and arrange them on a large baking tray lined with parchment paper or a silpat liner.
Crimp the outside of the dough with a fork.
Lightly brush the top of each pie with the egg yolk/water mixture.
Use a paring knife to make a couple small slits in the top of each pie so steam can escape.
Bake the pies until they’re golden and flaky, about 25 to 30 minutes at 375F, rotating the tray once halfway through.