preheat the oven to 400°
lightly butter the casserole dishes and set them on a lined baking sheet
in a bowl, mix the cooked chicken together with the cooked vegetables
heat the gravy until it's hot
mix the gravy with the chicken and vegetables
divide the mixture between the two dishes, set aside
cut the piece of puff pastry in half, roll it out lightly to fit the top of the pot pie dishes
lay the dough over the chicken mixture, and gently pinch it around the top of the pan, you can fold the square corners in or under the dough or leave them out to get toasty and crispy
cut the top of the pie with a sharp knife to vent
beat the egg with a splash of water
brush the top of the pie with the egg wash
bake in the preheated oven until the top is cooked through, crispy, and browned, generally 25-30 minutes
let the pies rest for a couple of minutes before serving