Place the beef bones on a sheet pan and roast them at 350 degrees for 30 minutes. Remove the bones from the sheet pan and place into the stock pot. (The bones may give off some fat, don't add the fat to the broth.)
Add the chicken feet (or other parts) to the stock pot and cover everything with water.
Let the water come up to a boil then reduce the heat so the water is just simmering.
Some fat and foam will rise to the top, skim this off with a ladle. You should skim the surface of the stock occasionally during cooking but it will be most foamy during the first hour or two of cooking.
If you're using vegetables and vinegar add them after the first hour of cooking. If you add the vegetable too soon you may end up skimming them out when skimming the foam and fat.
Simmer on low heat for 8-10 hours. You may need to add a little water to keep the bones covered.
You can also put this all in a crock pot for 10 hours.
Strain the broth through a colander (lined with cheesecloth if you like) into another pot and chill it in a large container or sink filled with lots of ice and some water (ice water bath) to cool quickly. Stir the broth occasionally during cooling. Add more ice as it begins to melt.
Cool in the ice bath about 20 minutes
Pour the stock into storage containers
Label the containers with the date.
Store in the refrigerator for a week or freeze for a month.
If there is any fat in the broth it will rise to the top and solidify after refrigeration. You can easily remove the fat at this point.
Reheat and add desired flavorings such as lime juice, ginger, chili, garlic, lemon grass