Turkey Potpie with Cheddar Biscuit Crust Recipe

Ingredients

• Carcass and skin from a 12- to 14-pound roast turkey
• 10 cups water
• 1 medium onion, coarsely chopped
• 2 large carrots, cut into 1/2-inch pieces
• 2 celery ribs, cut into 1/2-inch pieces
• 1 large parsnip (peeled), cored and cut into 1/2-inch pieces
• 1 teaspoon chopped thyme
• 3 tablespoons unsalted butter
• 1/2 pound mushrooms, trimmed and quartered
• 1/4 cup all-purpose flour
• 4 cups roast turkey meat, cut into 1/2-inch pieces
• 1 (10-ounce) package frozen baby peas, thawed
• 2 cups all-purpose flour
• 2 teaspoons baking powder
• 1 teaspoon baking soda
• 1/2 teaspoon salt
• 1/2 teaspoon black pepper
• 1 cup coarsely grated extra-sharp Cheddar
• 1/4 cup grated Parmigiano-Reggiano
• 3/4 stick cold unsalted butter, cut into 1/2-inch pieces
• 1 1/4 cups well-shaken buttermilk