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Prime Rib Sandwich with Caramelized Onions and Horseradish Sauce

This dish features thin slices of tender, flavorful prime rib layered on bread with sweet, fragrant caramelized onions and a tangy horseradish sauce. The sandwich combines the rich, juicy texture of slow-cooked beef with the soft, toasted bread and smooth, savory toppings, creating a hearty and satisfying meal. The preparation emphasizes gentle reheating, careful caramelization, and balanced assembly to highlight each ingredient's depth.
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Prep Time 10 minutes
Cook Time 20 minutes
Total Time 30 minutes
Servings: 2
Course: Main Course
Cuisine: American
Calories: 650
Ingredients Equipment Method Notes

Ingredients
  

  • 4 slices prime rib slices preferably thinly sliced leftover roast
  • 1 large yellow onion sliced thinly
  • 2 tablespoons butter
  • 2 teaspoons balsamic vinegar optional, for enhanced sweetness
  • 2 tablespoons horseradish sauce prepared horseradish mixed with mayonnaise or sour cream
  • 4 slices bread such as baguette or sandwich bread, toasted lightly

Equipment

  • Skillet or frying pan
  • Knife
  • Cutting board
  • Toaster or oven

Method
 

  1. Heat a skillet over medium-low heat and add butter, allowing it to melt and sizzle softly. Once melted, add the sliced onions and cook slowly, stirring often, until they soften and turn a deep golden brown, about 15 minutes. The onions should smell sweet and caramelize evenly.
  2. After the onions have caramelized, splash in the balsamic vinegar and stir quickly to deglaze the pan, pulling up any browned bits. Let the mixture simmer for a minute until the vinegar reduces slightly and the onions absorb the sweetness.
  3. While the onions are cooking, gently reheat the prime rib slices in a separate pan or in the microwave until warm. Keep the slices tender—avoid overcooking or drying them out.
  4. Toast the bread slices lightly until golden and crispy on the edges. You can do this in a toaster or in a pan with a little butter for extra flavor.
  5. Spread a generous layer of horseradish sauce on one side of each toasted bread slice, adding a spicy tang to balance the savory beef and sweet onions.
  6. Layer the warmed prime rib slices over the horseradish-spread bread, then top with a handful of caramelized onions for sweetness and texture.
  7. Close the sandwich with the second slice of bread, pressing gently to hold everything in place.
  8. Cut the sandwich diagonally or in half, if desired, and serve immediately while the bread is crispy and the filling is warm and tender. Enjoy the hearty flavors and contrasting textures!

Notes

Ensure the onions are caramelized slowly for maximum sweetness. Use leftover prime rib slices for quick assembly. Feel free to add pickles or arugula for extra freshness.