Preheat oven to 400° degrees.
Heat a large saute pan over medium heat and add in the butter. When the butter has just melted, stir in the onion, carrot, celery, and spice rub. Cook, stirring occasionally, for 5-8 minutes or until the vegetables are soft. Stir in the minced garlic and cook for another minute.
Sprinkle the flour over the vegetables and stir to combine, leaving no white flour visible. Let cook for a minute, then stir in the broth, scraping the bottom. Stir well with a wooden spoon or even a whisk so that no lumps remain. Let the mixture come to a simmer so it starts to thicken and cook for 2-3 minutes. When it reaches a thicker, sauce-like consistency, stir in the milk and marinade. Let the mixture come to a simmer and thicken up a bit again, then stir in the turkey and frozen vegetables (if using). Lower heat to medium-low, simmer for another 5-10 minutes, then remove from heat and let cool for a few minutes. Season to taste with salt and pepper.
Spray or grease a 9-inch pie pan (metal or glass, if using); use pre-made crusts as directed on the package. Fill bottom pie crust (or empty pie pan if doing single crust) with filling to the brim of the crust. Set top crust on top of the filling; if using a double crust, pinch together both crusts. Brush the crust with melted butter or egg wash, make a few slits in the top, and bake for 35-45 minutes or until the top is golden-brown and the filling is bubbling. If the edges of the crust look like they're getting too dark while it's baking, simply cover them with foil.
For individual pot pies: Cut crusts to fit over large ramekins or small soup cups (crust should be slightly larger than the opening of the cup). Fill vessels almost to the brim with the cooked filling, then top with the individual crusts. Make slits in the crusts, brush with butter or egg wash, and bake 20-25 minutes. Optional: Melted butter or egg wash (1 egg beaten with 1 tablespoon water) for brushing on top of the crust