1. 1. Saute the Aromatics: In a large oven-safe skillet or Dutch oven (at least 9-10 inches in diameter and 2 inches deep), melt the unsalted butter over medium heat. Add the chopped yellow onion and carrots, cooking for about 5-7 minutes until they are softened and the onion is translucent. This step builds the foundational flavor of your pot pie.

2. 2. Add the Remaining Vegetables: Stir in the frozen peas and corn. Cook for another 2-3 minutes, allowing them to warm through. The vibrant colors of the vegetables will start to pop, indicating they are ready for the next stage.

3. 3. Create the Roux and Liquid Base: Sprinkle the all-purpose flour over the vegetables and stir constantly for 1 minute. This creates a roux, which will thicken your sauce. Gradually pour in the turkey or chicken broth, whisking continuously to prevent lumps. Once smooth, slowly add the milk, continuing to whisk until the mixture begins to thicken and bubble gently.

4. 4. Incorporate Turkey and Seasonings: Add the shredded or diced cooked sourdough turkey, dried thyme, and dried sage to the thickened sauce. Stir everything together until the turkey is well coated and the mixture is evenly combined. Season generously with salt and black pepper to taste. The filling should be rich and creamy at this point.

5. 5. Prepare the Puff Pastry Topping: Carefully unroll the thawed puff pastry sheet. If your skillet is round, you can use a plate or the skillet itself as a guide to cut the pastry into a slightly larger circle than the top of your skillet. If using a rectangular baking dish, simply place the pastry over the top. Gently drape the puff pastry over the hot turkey filling in the skillet, pressing it lightly around the edges to seal. You can crimp the edges for a decorative touch.

6. 6. Egg Wash and Venting: In a small bowl, beat the large egg. Brush the top of the puff pastry with the beaten egg wash; this will give it a beautiful golden sheen. Using a sharp knife, cut a few small slits in the center of the pastry to allow steam to escape during baking, preventing it from puffing up too much in the middle.

7. 7. Bake Until Golden: Place the skillet into a preheated oven at 400 F (200 C). Bake for 25-30 minutes, or until the puff pastry is deeply golden brown and beautifully puffed, and the filling is bubbling around the edges. The visual cue of a golden, flaky crust is your signal that it’s perfectly done.

8. 8. Rest and Serve: Carefully remove the pot pie from the oven. Let it rest for 5-10 minutes before serving. This allows the filling to set slightly and prevents burns from the hot, bubbling sauce. Serve warm and enjoy your comforting creation!