Preheat the oven to 375°F. Heat 2 tablespoons of bacon fat in a large pan and sauté diced onions, celery, and green peppers. Season with salt and pepper, and cook until vegetables release their juices (about 5 minutes).
In a large bowl, combine shredded turkey, sautéed vegetables, and peas.
Add crumbled cornbread, stuffing mix, and 4 cups of turkey stock. Stir well.
Mix in sage, poultry seasoning, and melted butter, followed by the remaining 4 cups of stock. Stir until fully combined.
Spray two half-sheet pans with cooking spray and divide the dressing evenly between the pans.
Bake for 30 minutes, then rotate the pans and bake for another 30 minutes or until the dressing is crispy around the edges.
It's almost impossible (within reason) to overcook this, so you may want to leave it in longer if you prefer crispier edges like my family.