In a large pan at least 1 inch deep - place your beef bones - bake for 3 hrs at 425°F Remove and cool. Ask your butcher, short bones work as well some meat left on the bone is fine some even like using the oxtail bone, any is really ok.
Place in a large stock pot and cover with 12 cups of water. Add salt, pepper, thyme and bay leaves - slow cook for 3 hours. Remove bones and herbs.
You should be left with a nice dark rich color beef stock - this can be sealed in jars or frozen for later use. The heartier the stock the better the soup.