Preheat oven to 400° F.
Place the beef marrow bones on a baking tray and roast for 20-25 minutes, or until the marrow is soft and slightly golden.
In a large saucepan, heat the olive oil over medium heat. Add the onion and garlic and cook until softened, about 5 minutes.
Add the Arborio rice and stir to coat in the oil. Cook for 1-2 minutes, or until the rice is translucent.
Pour in the white wine and stir until it has been absorbed by the rice.
Slowly add the beef or chicken stock, one ladleful at a time, stirring continuously, until the liquid has been absorbed before adding the next ladleful.
Once the rice is cooked and the risotto is creamy, remove from heat. Stir in the butter and Parmesan cheese.
Season with salt and pepper to taste.
Use a spoon to scoop the marrow out of the bones and add it to the risotto, mix well.
Serve the risotto in bowls, garnished with fresh parsley, if desired.
Enjoy!