Melt butter in a 3-quart pot over medium heat. Add onions, celery, and garlic and sauté for 2 minutes until the onion is translucent.
Add chicken, carrots, peas, broth, salt, pepper, and dried thyme.
Cook for 10 minutes until the vegetables have cooked through.
In a slow, steady stream, pour in the heavy whipping cream. Sprinkle the cheddar cheese and stir to mix. Allow the soup to simmer gently for 5 minutes and then serve hot.
For The Crust And Assembly
Preheat your oven to 4000F.
Place your prepared filling into a casserole dish.
Lay the sheet of refrigerated pie dough over the top of your filling.
Secure the edges of the pie crust to the casserole dish using a fork or pie crimper.
Beat an egg and use the egg wash to gently brush the top of the pie crust.
Cut a few slits in the top to allow steam to release.
Bake the Chicken Pot Pie Casserole for 15-20 minutes or until golden brown and flaky.