Thaw frozen peaches completely in a colander set over a bowl for 2-3 hours or overnight, then press gently to remove excess liquid and blot dry with paper towels.
In a large bowl, combine drained peaches with sugar, cornstarch, cinnamon, nutmeg, lemon juice, and vanilla. Stir gently and let rest for 15 minutes, then taste and adjust sweetness if needed.
Preheat oven to 400°F (200°C) and place a rimmed baking sheet on the lower rack. Lightly grease a 9-inch deep dish pie pan.
Roll out the first pie crust to a 12-inch circle and carefully fit it into the pie dish, pressing gently into the bottom and up the sides without stretching the dough.
Pour the peach filling into the crust, spread evenly, and dot with small cubes of unsalted butter.
Roll out the second crust and place it over the filling. Trim, fold, and crimp the edges to seal. Cut steam vents or create a lattice top with strips of dough.
Brush the top crust with egg wash (1 egg beaten with 1 tablespoon water) and sprinkle with turbinado sugar.
Bake at 400°F for 20 minutes, then reduce temperature to 375°F and continue baking for 35-45 minutes until the crust is golden and filling is bubbling with thick, jam-like bubbles.
Cool the pie on a wire rack for at least 2 hours before slicing to allow the filling to set properly.