Preheat your oven to 400°F. In a small bowl, whisk the beaten egg with 1 tablespoon of water to make an egg wash and set it aside. This will be used to help seal the pie and give it a golden finish.

In a medium saucepan, melt the butter over medium-low heat. Add the diced onion and sauté until tender, about 5 minutes. Stir in the flour, poultry seasoning, thyme, and a pinch of salt and pepper. Cook this mixture for 2 minutes, stirring frequently, to form a flavorful roux.

Gradually whisk in the chicken broth and milk or cream, a little at a time, stirring after each addition until smooth. The mixture will be thick at first but will smooth out as you add liquids. Bring to a boil over medium heat, then reduce to a simmer for 1 minute until the sauce thickens. Remove from heat. Stir in the cooked chopped turkey, thawed frozen vegetables, and diced potato until everything is well combined. I always taste the filling now and adjust the seasoning if needed.

Line a 9-inch pie plate with one of the pie crusts. Fill the crust with the warm turkey filling from Step 3, spreading it evenly. Brush the edges of the crust with some of the egg wash from Step 1. Place the second pie crust over the filling, then pinch the edges to seal. Cut a few small slits in the top crust to vent steam. Brush the top of the pie with the remaining egg wash for a beautiful golden crust.

Place the assembled pie on the center rack of the oven and bake for 35-40 minutes, or until the crust is lightly browned and the filling is bubbly.

Let the pie cool for 10-15 minutes before cutting into slices. This helps the filling set and makes serving much easier. I find that waiting a bit really helps keep the slices neat.