A tasty new stuffing from Michael Symon!

4 tablespoons unsalted butter (plus more for greasing)
8 cups sourdough bread (medium dice)
1/4 cup olive oil (divided)
1 cup onions (peeled, finely diced)
1/2 cup celery (finely diced)
1/2 teaspoon celery seeds
2 cups Brussels sprouts (thinly shaved on a mandoline)
4 cups mixed mushrooms (stems removed, sliced)
2 cups chicken stock
2 large eggs (slightly beaten)
2 tablespoons parsley (finely chopped)
Kosher salt and freshly ground pepper (to taste)

Preheat your oven to 375ºF degrees. Butter a casserole dish and set aside.
Place the bread cubes on a baking sheet and place in the oven to toast until light golden brown and dried out, about 10 minutes. Remove the bread to a large mixing bowl.
In a large saute pan over medium heat, add the 4 tablespoons butter, 2 tablespoons of olive oil, onions, celery and celery seeds. Season with salt and pepper to taste. Cook, stirring occasionally until the vegetables start to soften, about 3-5 minutes. Stir in the Brussels sprouts, and continue to cook until the Brussels sprouts have softened, about 5 minutes. Stir the mixture into the bread.
Place the pan back on the heat, add the remaining olive oil and the mushrooms in a single layer and cook until golden brown and crisp, about 5-7 minutes. Season with salt and pepper, then add to the bread mixture, stirring to combine. Add the chicken stock, eggs and parsley and stir to thoroughly combine. Season well with salt and pepper, then let the mixture sit in the bowl for 10 minutes to allow the bread to hydrate.
Pour bread mixture into the casserole dish, cover with foil and bake for 30 minutes. Remove the foil and continue to bake for another 15-20 minutes to crisp the top. Remove from the oven and serve.
Tip: Instead of buying a new loaf of bread, use the any old bread that has gone stale!