Classic Demi-Glace

Instructions

1. Roast the bones
   Preheat oven to 450°F (230°C). Place beef marrow and veal knuckle bones in a large roasting pan and roast for 45 minutes until deeply browned, turning occasionally.
2. Prepare the mirepoix
   Add carrots, onions, celery, and leek to the roasting pan with bones for the final 20 minutes of roasting until vegetables begin to caramelize.
3. Create the brown stock
   Transfer bones and vegetables to a large stockpot. Add 16 cups of cold water, garlic, bay leaves, peppercorns, thyme, and rosemary. Deglaze the roasting pan with red wine, scraping up all browned bits, and add to the stockpot.
4. Simmer the stock
   Bring to a boil, then reduce heat to low. Simmer uncovered for 4-5 hours, occasionally skimming off any foam or impurities that rise to the surface. The liquid should reduce by about half.
5. Make the espagnole sauce
   In a separate saucepan, make a brown roux by cooking flour in 1/4 cup of fat skimmed from the stock until nutty brown. Gradually whisk in 4 cups of the strained stock. Add tomato paste and simmer for 45 minutes, skimming occasionally.
6. Reduce to demi-glace
   Combine the espagnole sauce with an equal amount of remaining stock. Simmer gently for 1-1.5 hours until reduced by half and thick enough to coat the back of a spoon.
7. Strain and finish
   Strain the demi-glace through a fine-mesh sieve lined with cheesecloth. Return to a clean saucepan and simmer for a final 15 minutes to adjust consistency if needed.