While the cornbread bakes, prep and chop all onions, celery, peppers, shallots, and garlic.
Preheat oven to 350°F.
Place a large skillet over medium-high heat and add 1 tbsp EVOO. Once hot, add onions, celery, peppers, shallots, and garlic. Sauté until onions are soft and translucent. Remove from heat and set aside.
When the cornbread is cool enough to handle, crumble it into a large mixing bowl.
Add the sautéed vegetables.
Add: salt, onion powder, Old Bay, black pepper, thyme, and sage. Mix until combined. If using Pepperidge Farm stuffing, mix it in at this stage.
Pour in 3 cups of chicken stock and ½ stick of melted butter. Stir well. The mixture should be moist but not soupy. If it feels dry, add a splash more stock.
Spoon the mixture into a large baking dish.
Press the sliced butter pieces around the edges of the dish (this gives you those crispy, buttery corners).
Bake at 350°F for 1 hour. If it starts browning too fast, tent the pan with foil.