1.
Preheat the oven to 190 C / Gas 5.
2.
Cut the marrow in half lengthways. Scoop out the seeds, and discard. Scoop out the flesh, and chop finely. Leave about 1cm of flesh in the marrow halves. Place the two halves in a suitable baking dish that's been lightly greased.
3.
Mix the chopped marrow flesh with the sausagemeat, onion, garlic, breadcrumbs and Parmesan cheese. Season to taste with salt and pepper. Stuff marrow halves with the sausagemeat mixture. Pour pasta sauce over the marrow and cover baking dish with foil.
4.
Bake in preheated oven for 45 minutes, or until sausagemeat is cooked. Remove foil and cover with mozzarella cheese. Cook until cheese is melted.