01 - Preheat oven to 430°F. Place beef bones and shank on a roasting pan and roast for 30-40 minutes, turning once, until deeply browned.
02 - Transfer roasted bones and meat to a large stockpot. Deglaze roasting pan with a little water, scraping up browned bits, and pour into the pot.
03 - Add onions, carrots, celery, leek, garlic, tomato paste, bay leaves, thyme, peppercorns, and parsley stems to the pot.
04 - Cover ingredients with cold water and slowly bring to a gentle simmer over medium heat. Skim foam and impurities during the first 30 minutes.
05 - Reduce heat to low, cover loosely, and simmer for 4 hours, occasionally skimming fat and scum. Avoid boiling vigorously.
06 - Strain stock through a fine-mesh sieve into a clean pot or bowl, discarding solids.
07 - Cool stock quickly and refrigerate. Once chilled, remove hardened fat from the surface.
08 - Add salt to the stock only when ready to serve or use.