First, add beef bones to a large stockpot and cover with water. Bring to the boil. You will start seeing impurities come to the top. Boil for 5 minutes and scoop out everything that floats to the top. Repeat 3 times cooking for 5 minutes each time.
Remove beef bones and discard liquid. Clean stockpot really well.
Option: You could roast the onions, carrots, and celery in the oven until tender. Adds flavor, but not needed.
Place beef bones on a cookie sheet covered with aluminum foil. Helps with the roasting and clean up.
Roast bones in oven at 450 degrees for 30 minutes. Next paint on tomato paste to the tops "only" of the beef bones and place back in the oven for an additional 20 minutes.
Place all roasted beef bones, onion, carrots, celery & Sachet into a large stockpot and cover with water.
Bring to boil and turn down heat to low and cover.
Cook for 36 hours then remove the cover and allow to reduce, but do not turn up the temperature. Slow reduction.