Prepare Pie Crust: Start by making your pie crust according to the recipe, chilling it for a minimum of 2 hours. This recipe requires two crusts: one for the base and another for the top.
Cook Chicken and Veggies: Place cubed chicken, carrots, and celery in a large pot. Cover with water, bring to a boil over medium-high heat, and cook for 10 minutes. Drain and set aside after boiling.
Make the Gravy: In a skillet over medium heat, melt butter and cook onions and garlic until soft. Blend in flour, seasonings, chicken broth, and half-and-half, stirring until thickened into a gravy, about 10 minutes.
Preheat the Oven: Set your oven to 425°F (218°C) to preheat.
Roll Out and Fit Bottom Crust: Roll one pie dough disc into a 12-inch circle and place it into a 9-inch pie dish, trimming excess dough from the edges.
Assemble the Pie: Layer the drained chicken and vegetables into the bottom crust, add frozen peas, and pour the gravy on top.
Add Top Crust and Apply Egg Wash: Cover with the second rolled-out pie dough, seal the edges, and cut slits in the top. Brush with an egg wash for a golden finish.
Bake the Pie: Bake for 32–38 minutes, covering the crust edges with foil if they brown too quickly, until the crust is golden.
Cool Before Serving: Let the pie cool for at least 10 minutes to set before serving, ensuring a perfect slice.