Preheat the oven to 250°F. Crumble the muffins onto a baking sheet and bake for 30-40 minutes or until dried. Alternatively, leave out overnight uncovered. Pour into a large mixing bowl.
Spray an 8x8-inch casserole dish with cooking spray. Preheat the oven to 350°F.
Melt the butter in a large skillet over medium heat. Add the onions and celery and cook, stirring occasionally, until softened, about 8 minutes. Add the garlic and poultry seasoning and cook, stirring, for 30 seconds. Add to the dried, crumbled muffins and stir. Add the stock, stir, and season to taste with salt and pepper. Stir in the eggs and mix well. Put the stuffing in the prepared casserole dish, cover with foil, and bake for 30 minutes. Remove the foil and continue to bake for another 5-10 minutes or until golden on top.