01 - Preheat oven to 425°F. Place beef bones and shank on a roasting pan and roast for 30 to 40 minutes, turning once, until deeply browned.
02 - Transfer roasted bones and meat to a large stock pot. Pour off fat from the pan, add a little water to loosen browned bits, then scrape and add these to the pot.
03 - Add onions, carrots, celery, leek, and garlic to the pot.
04 - Stir in tomato paste if using, to deepen color and flavor.
05 - Add enough cold water (about 12.7 cups) to cover the ingredients completely. Slowly bring to a simmer over medium heat.
06 - During the first 30 minutes of simmering, skim off any foam or impurities that rise to the surface.
07 - Add bay leaves, thyme, parsley stems, peppercorns, cloves, and salt to the pot.
08 - Partially cover and simmer gently without boiling for 4 hours, skimming the surface occasionally.
09 - Strain the stock through a fine-mesh sieve or cheesecloth into a clean container, discarding solids.
10 - Cool quickly, refrigerate, and once chilled, remove solidified fat if desired. Use immediately or store refrigerated for up to 5 days or freeze up to 3 months.