• Preheat the oven to 425°F.
• Dice the onion and cooked chicken or turkey. Set aside.
• Place the frozen vegetables in a colander and rinse under cool water to remove any ice. Drain well.
• In a heavy-bottom pot over medium heat, melt the butter. Whisk in the flour to form a roux.
• Add the diced onion, salt, and pepper. Continue whisking and cook for 1–2 minutes, until the onions begin to soften.
• Slowly whisk in the milk and broth. Continue whisking until the mixture comes to a low boil and thickens.
• Stir in the drained vegetables and diced chicken. Remove from heat and set aside.

Assemble the Pot Pie

• If using 9-inch pie pans, this recipe makes enough filling for two pies. If using a 9x13-inch baking dish, use two sheets of puff pastry rolled out and pressed together for the bottom, and two sheets for the top.
• Butter the pan well. Place the bottom crust in the pan, pressing it gently into place.
• For pie pans, fill each pan halfway with the chicken and vegetable mixture. For a 9x13 dish, pour all of the filling into the pan and spread evenly.
• Place the top crust over the filling. Seal the edges by crimping with a fork or pinching the dough together. Cut a small X in the top crust to allow steam to escape.

Baking the Pot Pie

• In a small bowl, beat the egg with 1 tablespoon of water. Brush the egg wash evenly over the top crust.
• Bake at 425°F for 15 minutes, then reduce the oven temperature to 375°F and continue baking for 20–35 minutes, or until the crust is golden brown and the filling is bubbling.
• If the edges begin to brown too quickly, loosely cover them with foil.
• Remove from the oven and let cool for 10–15 minutes before slicing and serving.