Soak the marrow bones in plenty of cold water in a covered container in the fridge for 24 hours, changing the water three times. Using either your finger or a wooden spoon handle, poke the marrow out of the bone. Be careful of very sharp, fine shards of bone which occasionally make themselves known. Rinse the marrow in gently running cold water for a few minutes, then carefully go over them to make sure no bone is attached. Measure out
Put the butter in a wide pan and cook it on a medium-high heat to a beurre noisette stage (until it turns nutty brown in colour). Add the sliced marrow and cook for 1½ minutes, stirring as it melts down, although there will still be lumps.
Add the breadcrumbs and pine nuts and cook for another 2 minutes, stirring the whole time.
Take off the heat and stir in the Parmesan, parsley, garlic and lemon zest. Taste for seasoning, adding plenty of freshly ground black pepper.
Spoon into the warmed marrow bones and serve with hot toast, or simply serve in a ramekin alongside hot toast.
© 2010 Peter Gordon. All rights reserved.