In a medium saucepan, add 1¼ cups of red wine, a sprig of thyme, 1 bay leaf, and 2 tablespoons of minced shallots. Turn the heat to high and bring the mixture to a rolling boil. Once boiling, reduce the heat to medium-low and let it simmer gently for about 15-20 minutes, stirring occasionally, until the liquid reduces to approximately ⅓ cup.

While the wine mixture simmers, take 1 pound of beef bones and extract the marrow. Place the marrow into a separate saucepan along with 15 ounces of low-sodium beef broth. Cover the pan and simmer on low heat for about 5 minutes, allowing the marrow's richness to infuse into the broth.

After simmering, remove the bone marrow from the broth and allow it to cool slightly. Using a sharp knife, finely mince the marrow into small pieces.

Once the wine reduction reaches the desired concentration, add your demi-glace to the saucepan. Stir well to combine, and then season the sauce with freshly ground pepper to taste. Lower the heat and allow the mixture to simmer on low for about 10-15 minutes.

After simmering, remove the saucepan from heat. Pour the sauce through a fine mesh strainer into a clean bowl, pressing the solids with a spoon to extract any remaining liquid. Stir in your finely minced bone marrow before serving.