Ian Conway on Instagram: "How to PROPERLY Reheat Leftover Steak Ingredients - Leftover steak or prime rib - Sweet onion, thinly sliced - Swiss or Provolone cheese - Beef Au Jus or beef broth or gravy - French rolls or baguettes - Olive oil - Butter - Salt - Pepper - Mayonnaise - Whole grain mustard - Worcestershire Directions Start out by adding your onions to a pan with butter and olive oil. Keep the heat on low and season your onions with salt, pepper and brown sugar. Slowly cook down your oni