Heat the oven to 375°F and prepare your muffin tins. Spritz the inside of the muffin molds with non-stick cooking spray and set aside, away from the preheating oven so that they stay room temperature.
Work with the pie dough in batches, keeping unused portions in the fridge to keep cold. Roll out the dough on a well-floured surface to a thickness of about 1/8 inch. Using a cookie cutter or stencil, cut out 6-inch circles from the dough and press them gently into each muffin cup – You should use about two-thirds of the dough for the bottom crusts. The circles don’t have to be perfect, but you should try to have at least a quarter inch of dough overlapping the top of the cups.
Fill each crust nearly to the top with about 2 spoonful’s of the chilled filling and place the muffin tin back into the fridge to keep cold as you prepare the pastry lids.
Roll out the remaining third of the pie dough to the same thickness as the bottom crusts and cut out 3-inch circles. Set the pastry lids out on a tray or baking sheet, and cut hashmarks in the centers to allow for steam to vent while cooking.
Remove the chilled muffin tins from the fridge. Working one at a time, place each pie top over the filling of each pie. Crimp the edges of the pie over the lid, sealing them tightly. Once all the pies are constructed, brush the tops with egg wash.
Bake the chicken pies for 30-40 minutes, until the tops are golden. Remove from the oven, and let them sit for 10 minutes before gently removing them from the muffin tins. Serve warm, or follow instructions below for cooling and storage.