Heat the oven to 180 degrees C
In a large heavy bottomed saucepan, heat the olive oil
Fry the onion until soft
Add the garlic
Add the beef mince an cook for a few minutes until brown
Add the tomatoes, herbs and tomato puree
Cook for 20 minutes
Meanwhile, scoop out the middles of the marrow rings
Place them in a large baking dish
Spoon a portion of the mince sauce into each
Distribute the remainder over the top of the marrow rings
Cover with foil and bake in the oven for about 30 minutes
Remove the foil, sprinkle with cheese and return to the oven uncovered for 10 minutes