1-First, caramelize the onions by melting 2 tablespoons of butter in a skillet over medium-high heat. Add the 2 large thinly sliced yellow onions in a single layer without stirring at first, then gradually reduce the heat and stir only when they begin to brown, cooking until they turn a dark caramel color, and set them aside.

2-Next, mix 2 tablespoons mayonnaise with 1 teaspoon creamy horseradish to create a spread; you can add the 16 cloves roasted garlic whole or mash them in for extra flavor. Dress 2 cups arugula with 1 teaspoon olive oil and 1 teaspoon white balsamic vinegar or lemon juice, and season with salt and pepper if you like.

3-Now, assemble the sandwiches by layering the horseradish mayo spread, dressed arugula, 12 ounces sliced prime rib, and caramelized onions between 8 slices of sourdough or baguette bread. The sandwich works best served cold to keep the meat tender, though you can warm the meat slightly if you prefer. For more ideas on sandwiches, check out our grilled chicken sandwich recipe for a tasty variation.