Brown the beef bones and put them in a large stockpot. Cover with water and boil. Keep the bones covered with water for 8 to ten hours.

Strain, reserving the liquid.

Put the beef bones in the pot with the chicken bones, vegetables and seasonings. Cover with water and cook for 4 to 5 hours.

Strain, reserving the liquid.

Combine both the beef liquid and the chicken liquid together. Bring to a boil and then add the tomato puree. Cook for 10 minutes, then strain.

Increase heat and reduce until the liquid will coat a spoon.

Skim the surface of the mixture throughout the reduction.

Any leftover demi-glace can be frozen in an ice cube tray and used a cube at a time later....