Review instructions for brown beef stock preparation.
Place (unwashed) bones in a roasting pan in a hot oven (about 425F) and brown for about 1 hours, until nicely browned.
Transfer the bones from the roasting pan to a stockpot. Cover with water and bring to a simmer. Skim and let stock continue to simmer.
Remove and reserve the fat from the roasting pan. Deglaze the pan with water and add to stockpot.
Put the mirepoix and some of the reserved fat into the roasting pan and brown well in oven. Add tomato paste to mirepoix. Continue to brown until tomato paste turns a rusty brown color.
Add browned mirepoix, tomato product, and sachet to the stockpot.
Continue to simmer for 6-8 hour for veal bones and 8-10 hours for beef bones, keeping the bones covered with water.
Strain through several layers of cheesecloth.
Cool the stock in an ice bath, then refrigerate or freeze.