Heat the olive oil in a large pan or pot over medium heat. Add the carrots, onions, and celery, and cook until golden brown and translucent, 5 minutes. Season very lightly with salt and pepper.
Add the sausage and beef. Season very lightly with salt and pepper again, then break up the sausage into small chunks and cook for 3 minutes.
Add the wine and reduce by half, 1 minute or so, then add the marrow bone if using, making small pools so that the bones sit on the bottom of the pot. Add the tomatoes, rosemary and bay leaf, and enough stock to cover the top of the marrow bones, about 1 cup.
Turn the heat up to high to bring to a boil, then reduce the heat down to low and cover. Simmer for 2 hours. Check for seasoning and add salt and pepper as needed.
When you are ready to eat, pop out the bone marrow with a small spoon or the back of a wooden spoon and stir it in along with the cheese over low heat. Cook your pasta 1 minute shy of al dente, then drain and transfer to sauce. Toss lightly, then serve with chopped rosemary, pepper flakes, and cheese, as desired.