Sourdough, Italian Sausage, and Chestnut Stuffing

Preheat oven to 350 °. Butter a shallow 3-quart baking dish and a sheet of foil. Place bread in a very large bowl. Heat 2 tablespoons oil in a small saucepan over medium heat. Add chestnuts, season with salt and pepper, and cook, stirring often, until chestnuts are golden and crisp, about 5 minutes. Transfer to bowl with bread with a slotted spoon. Heat remaining 1/4 cup oil in a large skillet over medium-high. Add sausage and cook, stirring occasionally and breaking into small pieces with a wooden spoon, until browned and cooked through, 8 –10 minutes. Transfer to bowl with slotted spoon. Add onions, celery, and chiles to skillet, season with salt and pepper, and cook, stirring often, until onions are translucent and soft, 5 –7 minutes. Add apple, garlic, and sage and cook, stirring occasionally, until onions are golden brown and apple is soft, about 5 minutes. Discard chiles. Add onion mixture to bowl. Add onions, celery, and chiles to skillet, season with salt and pepper, and cook, stirring often, until onions are translucent and soft, 5 –7 minutes. Add apple, garlic, and sage and cook, stirring occasionally, until onions are golden brown and apple is soft, about 5 minutes. Discard chiles. Add onion mixture to bowl. Reduce heat to medium and cook Sherry in skillet, scraping up any browned bits, until almost all evaporated, about 1 minute. Add 1/2 cup butter; cook, stirring, until melted. Drizzle over bread mixture. Whisk eggs and 2 cups stock in a medium bowl; pour over bread mixture. Season with salt and pepper and toss, adding more stock 1/4-cupful at a time as needed (you may not use it all), until combined and bread is hydrated. Transfer to prepared dish and dot with remaining 1/4 cup butter. Cover with buttered foil; bake until a paring knife inserted into the center comes out hot, 30 –35 minutes. Increase oven temperature to 450 °. Uncover and bake until top is golden brown and crisp, 20 –25 minutes. Let sit 10 minutes before serving. Do ahead: Stuffing can be assembled 1 day ahead. Cover and chill.