We started making marrow bones about 5 years ago after one of my favorite restaurants took it off their menu. The bone selection is key to making sure you get solid offering of marrow.
7-10 lbs of marrow bones from GF animals (Ask your butcher for pieces cut from the center of the leg bone, where the ratio of marrow to bone is highest.)
Preheat the oven to 450 degrees. Place bones standing up in a roasting pan; add a big dash of salt and a pad of butter on the top of each bone. Cook for 15-25 minutes, or until they turn brown and start to pop!
Serve immediately and of course this just serves one.