Prep: Cut bread into 1 inch cubes. Spread onto a baking sheet, cover with a clean towel, and let sit on the counter overnight, until stale. (For a quicker alternative, place the baking sheet with the bread cubes in the oven while it preheats to dry them out).
Veggies: Preheat oven to 400°F (204°C). Heat 2 Tbsp of oil or butter in a large saute pan over medium heat. Add the mushrooms, cooking until they sweat out their moisture and become soft, about 5 to 7 minutes. Add onion, celery, carrots, and garlic, cooking until veggies are soft, about 10 more minutes.
Assemble: In a large bowl, drizzle remaining butter (melted) or oil over bread cubes, tossing to coat. Add cooked veggies, parsley, and spices, tossing again to combine*. Drizzle in broth and briefly stir to combine.
Bake: Transfer mixture to a greased casserole dish, optionally brushing with melted butter to create a more golden crust. Tightly cover with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 20 minutes, or until top is golden and crispy.
*If making ahead, stop at this point and transfer to the fridge. When ready to bake, stir in the broth and bake as instructed.Love herbs? This recipe is also great with fresh rosemary!