Preheat oven to 400° F. Place bones on a foil-lined tray. Roast bones, uncovered, until brown on all sides, turning every 20 minutes for approximately 1-2 hours, depending on amount of bones. This is to enhance the flavor of the broth. It does not increase the medicinal value, so it is up to you whether you would like to skip this step.
In large stock pot, over medium heat add 1 T coconut oil and add bones to stockpot with 1 1/2 quarts of cold water, or enough to cover the bones. Slowly bring to a boil, then turn down and simmer gently. Add peppercorns and 2-3 teaspoons vinegar and lemon grass.
Cook half-covered (this will reduce water evaporation). Simmer lamb broth for 12-24 hours. Add more boiling water if necessary when simmering, in order to keep bones covered. Skim surface every half hour to remove scum - do not stir!
Add the carrots, celeriac, parsley, tomatoes during the last 2 hours of cooking. Then strain vegetables out and store broth.