1packagestore-bought pie crusts (2 crusts, one for top, one for bottom)
Preheat oven to 375 degrees. Grease a 9.5-inch glass pie pan.
Season chicken breasts liberally with salt on both sides, and with just a little bit of black pepper,.
Heat a large skillet to a medium heat. Once the skillet is hot. Add two teaspoons of olive oil. Cook the chicken until golden brown on both sides and cooked through, about 2-3. minutes on one side, 1-2 minutes on the other. Remove from pan and set aside.
Add remaining olive oil and butter to the same pan. Add celery, potato, carrot, onion and salt. Stir with wooden spoon. Sauté veggies until they are slightly softened, but not cooked through, about 2-3 minutes. Add flour. Stir to combine. Cook for 1 minute.
Turn the heat off and slowly whisk in chicken stock and whole milk, making sure there are no lumps. Whisk in sherry. Use a wooden spoon to scrape all the brown bits off the bottom of the pan. Bring the mixture to a boil, then reduce to a simmer. Simmer until very thick, 2-3 minutes. While the sauce and veggies are simmering, chop the chicken into bite-sized pieces. When the sauce is thick, add chicken and season to taste with PLENTY of salt and pepper. Add frozen peas in, stir. Set aside.
Whisk water and egg together in a small bowl. Place one crust in the bottom of the prepared pan. Pour the pot pie mixture on top. Brush the bottom crust with egg wash and cover with another crust. Fold the top crust under, sealing the top and bottom crust. Crimp edges of crust. Brush the entire top with more egg wash (be generous!). If desired, sprinkle with dried thyme. Use a sharp knife to cut vents in the top of the crust to allow steam to escape while baking,. Bake in the oven until top crust is golden brown and filling is bubbling, about 45 minutes. Cool for five minute before serving.
I like to add the chicken stock and milk to a liquid measuring cup and heat it in the microwave for 45 seconds so they are both warm,