Heat the butter in a large skillet over medium heat. Add the onions and garlic and stir to coat in the butter. Cook, stirring, until caramelized, 12 to 14 minutes.
Deglaze with the red wine, then bring to a boil and reduce, 2 to 3 minutes. Add the salt and pepper. Stir in the cream and remove from the heat.
Spread the Dijon mustard on one side of the toasted rolls and the peppercorn ranch on the other side. Add the leftover Prime Rib slices to the bottom halves of the rolls.
Heat a nonstick skillet over medium heat. Add the provolone to the skillet and let sit until melted, 1 to 2 minutes. Pour the cheese over the Prime Rib on both sandwiches. Top each with a good amount of the red wine onions and serve. |