From Italian trattorias to the ordinary American kitchen, spaghetti with tomato sauce is one of those timeless dishes that has a place on virtually every dinner table. But how do you keep a recipe that’s so well-worn exciting? You fill it out with flavorful ingredients. In this recipe, Italian sausage, mushrooms, and spinach are brought in to add an umami-packing boost and make the sauce rich, thick, and hearty. It’s comfortingly classic and familiar without being boring.