how to reheat prime rib
1 Place your leftover steak or prime rib in a piece of foil. 2  Then, using the au jus your steak came with, or a beef broth, use cover your steak in 2-3 tbsp worth.3  Hint: most restaurants provide au jus for prime rib and you can ask for a âto-goâ cup of it. Place your leftover steak or prime rib in a piece of foil. 2  Then, using the au jus your steak came with, or a beef broth, use cover your steak in 2-3 tbsp worth.