On a lightly floured countertop or board, unroll both of the pie crusts, but don't use a rolling pin to roll them any thinner.
Using a 4" biscuit or cookie cutter, cut as many circular crusts as you can from both pie crusts. You'll need 12 pie crust circles (generally 6 from each crust). Gather extra scraps and re-roll if needed.
To the center of 6 of the circles, add a dollop (I just use a small spoon, but it's probably about a tablespoon) of the cheesecake filling, then top with a dollop the same size of the blueberry pie filling.
You'll have pie filling and cheesecake filling leftover, but since the recipe calls for 1 egg, it can be difficult to split that in half, and the vast majority of pie filling comes in 21 oz cans. They'll both keep for a little while, or you can make multiple batches of hand pies!
Beat together the egg and 1 tsp milk (I just use a fork for this). Set aside. To the other 6 circles, cut 2 or 3 small slits in the center.
Brush the edges of the circles with filling with the egg/milk wash, then top with a circle with the slits. Gently press down to adhere the two circles together around the edges. Gently turn up the scalloped edges for a more secure and finished look.