This Prime Rib Sandwich is far and away the most delicious way to use up your prime rib leftovers. Juicy prime rib thinly sliced and served on a toasty baguette with caramelized onions, 2-minute horseradish mayo, melty Provolone cheese, and bright, peppery arugula -- it's quite literally the perfect bite. This steak sandwich recipe works great for any leftover cut of beef or steak; put it to use for just about and leftover beef recipe!
