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Close up of a prime rib sandwich on a black cutting board surrounded by au jus and beer.
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5 from 2 votes

Prime Rib Sandwich (Use Any Leftover Roast Beef)

Delicious prime rib sandwich using leftover Prime Rib Roast. You can use any leftover roast beef you have on hand.
Prep Time10 mins
Cook Time25 mins
Total Time35 mins
Course: Dinner, Lunch, Main Course
Cuisine: American
Keyword: Caramalized Onions, Garlic Bread, Pickled Pepper Recipes, Prime RIb, Prime Rib Recipe, Sandwich Recipe
Servings: 1 people
Calories: 1488kcal
Author: Darcey Olson
Cost: $5



  • 1 Small Onion, Sliced
  • 1 tbsp Unsalted Butter (*Note 2)
  • 1 tbsp Olive Oil


  • 2 Slices French or Italian Bread
  • 2 tbsp Unsalted Butter
  • 2 Cloves Fresh Garlic, Grated
  • Salt, To Taste (*Note 3)


  • 2 Slices Provolone or Swiss Cheese




  • Cut the onions into strips, uniform in size.
  • Add the butter and olive oil to a large skillet and heat over medium high heat.
  • Once the butter is sizzling add the onions and stir to combine.
  • Turn down the heat to medium and let the onions sit, uninterrupted, for about 5 minutes.
  • Repeat for about 20 minutes. If needed, add an additional tablespoon of butter or olive oil. If you see the onions are starting to burn, turn down the heat to medium low. Continue to stir every 5 minutes until you're left with golden caramelized onions.


  • While the onions are caramelizing, now is a good time to start the au jus, if making from scratch. If re-heating left over Au Jus, now is a good time to re-heat it and let is simmer until the sandwich is finished.


  • Once the onions and au jus are cooking, proceed to making the garlic bread. Pre-heat the oven to broil (High).
  • Add butter and grated garlic to a small bowl and stir to combine.
  • Slather equally on the 2 slices of bread. Set aside until ready to cook and assemble.


  • Place the 2 slices of bread, garlic spread side up on a cookie sheet and broil for approximately 3-4 minutes, until your desired brownness is achieved. Remove from oven.
  • Set aside one slice of bread. Top the second slice of bread with the leftover prime rib, caramelized onions and pickled peppers and broil for 3-4 minutes, until the meat is warm. Add the cheese to the top and broil, in the oven, for approx. 1-2 minutes, until melted. Keep your eyes on the cheese - it will melt quickly.
  • Remove from the oven and immediately top the sandwiches with the top slice of bread. Serve with the warmed au jus and enjoy immediately.


Note 1 - You can sub in any sliced beef for the prime rib. 
Note 2 - You can use salted butter, if that's what you have. 
Note 3 - You may or may not need extra salt. It depends how salty the beef is that you're using. I recommend waiting until the entire sandwich is pulled together, taste, and salt as needed.
Note 4 - You can use any type of pickled peppers. Both pickled banana peppers and pickled jalapeno peppers work great.
Note 5 - Feel free to use store bought au jus if you prefer to keep it easy.
Note 6 - We added arugula to the sandwich since we had some to use up. The sandwich is perfect without it. 
The nutritional calculations do not include any added salt, au jus or pickled peppers. 


Calories: 1488kcal | Carbohydrates: 85g | Protein: 50g | Fat: 106g | Saturated Fat: 50g | Polyunsaturated Fat: 6g | Monounsaturated Fat: 42g | Trans Fat: 1g | Cholesterol: 219mg | Sodium: 1076mg | Potassium: 787mg | Fiber: 5g | Sugar: 8g | Vitamin A: 1387IU | Vitamin C: 10mg | Calcium: 403mg | Iron: 8mg