1. Preheat oven to 450°F.
2. Dry the bones and season marrow side lightly with salt and pepper to taste.
3. Arrange marrow bones on a cooking tray or ovenproof pan, bone side down.
4. Roast until the marrow bones are lightly browned the marrow is soft and the fat just starts to bubble and separate from the bone, about 15-20 minutes.
5. Serve immediately with crusty bread and fleur de sel on the side.