I found these lovely marrows...here's the outcome:
Ingredients (serves 4)
1/2 kg of minced meat (beef or lamb)
1 large marrow
1 onion, finely chopped
2 cloves of garlic, finely chopped
lots of mint
Salt & pepper
Shallow-fry the onion and garlic in a pan. Add the minced meat and the mint and cook slowly. Add some tomato paste, cinnamon and nutmeg. Salt and pepper. In the meantime, cut the marrow in pieces roughly 4-5 cm thick (see pic). Hollow the pieces out by removing the seeds with a spoon. For the tips it's OK if there's no hole, make them like cups.
When the meat is ready, put the pieces of marrow flat in a pan and fill them with the minced meat. Fill them as much as possible. Add hot water in the pan, carefully and from the side so as not to make a mess with the filling. Add enough water to roughly half cover the marrow pieces. Allow to boil lightly, with the lid closed, for about 30 minutes. Check if the marrows cooked with a fork-if they're soft, they're ready. Serve them by carefully picking them up with a spatula underneath so the filling doesn't fall out.
Serve with cous cous or salad (or even both).