Mushroom and Rosemary Stuffing
Heat oven to 375° F. Heat the oil in a large skillet over medium heat. Working in batches, cook the mushrooms, tossing occassionally, until browned, 8 to 10 minutes. Transfer to a plate and reserve the skillet.
Butter a 9-by-13-inch baking dish. Divide the bread between 2 rimmed baking sheets and bake until dry and crisp, 10 to 12 minutes.
Meanwhile, wipe out the skillet and melt the butter over medium heat. Add the onions, celery, 1 teaspoon salt, and ¼ teaspoon pepper. Cook, stirring occasionally, until very tender and beginning to brown, 10 to 12 minutes. Add the sherry and cook until evaporated, 2 to 4 minutes; transfer to a large bowl and let cool for 10 minutes.