Once the onion is soft, add enough water to cover the meat. Bring this to a light boil and keep cooking until the water darkens.
[header] How to use leftover roast [title] Make beef broth. [step] You can make a rich beef broth to have on its own or use the broth as a base for soups and stews. To make the broth, just saute large pieces of the leftover roast beef along with one diced onion.