Preheat oven to 400°F.

Place beef bones in a roasting pan and roast for 1 hour until golden brown.

In a large pot or dutch oven, sauté onions, carrots, and celery until they begin to caramelize.

If using red wine, deglaze the pot with a splash of wine.

Add roasted bones, brown stock, espagnole sauce, tomato paste, and bouquet garni to the pot.

Bring mixture to a simmer and then reduce heat to low. Cover and let simmer for 4 hours, skimming the surface often.

After 4 hours, remove the pot from heat and let cool slightly.

Using a cheesecloth or fine mesh strainer, strain the demi glace into a clean pot or bowl.

Return the strained liquid to low heat and continue to reduce until desired thickness is achieved.

Use immediately or portion and freeze for future use.