Preheat the oven to 400°F (200°C). Grease a deep 9-inch pie plate with cooking spray or neutral oil. Then, whisk the egg and 1 Tablespoon (15 milliliters) of water in a small bowl to make egg wash.

Melt the butter in a 12-inch skillet over medium-high heat. Add the carrots, celery, shallots, and a big pinch of salt. Cook, stirring occasionally until the vegetables are tender and starting to brown on the edges, about 6-7 minutes. Add the garlic, thyme, and rosemary and sauté until fragrant, about 30 seconds.

Sprinkle the flour over the vegetable mixture, and cook for about 1 minute. Then, slowly whisk in the white wine, chicken broth, and milk until the mixture is smooth. Cook, stirring often, until the mixture is thickened and coats the back of a spoon.

Mix the potatoes, peas, and leftover turkey into the sauce. Season with salt and pepper, to taste. Carefully pour the filling into the prepared pie plate and let it cool slightly.

Next, unroll the puff pastry on a lightly-floured surface. Roll out any cracks in the pastry with a rolling pin. Using a pizza cutter or sharp knife, cut out a circle that's about 10-inches in diameter.

Stretch the puff pastry crust over the top of the filling and crimp the edges. Cut a few slits in the top of the pie for steam to escape. Then, use a pastry brush to brush the crust with the egg wash.

Bake the pot pie for 35-40 minutes until the crust is a deep golden-brown and the potatoes are tender. (If the crust starts to get too browned, tent the top of the pie with tinfoil.) Let the pot pie cool for about 10 minutes before serving. Enjoy!