Slice the baguette in half and then horizontally 3/4 of the way through with a bread knife.

Thinly slice the prime rib if needed and the onion.

In a small bowl, combine the 2 tbsp of butter with the 1 tsp of minced garlic.

Spread the garlic butter onto one-half of the sliced baguette halves and spread the mayonnaise on the other half. Set aside.

Add 2 tsp canola oil to a large skillet, add the sliced onions to the skillet and cook over medium heat, stirring often, until the onions are nicely caramelized. Transfer them to a bowl and set them aside.

Add the remaining 2 tsp of canola oil to the skillet, then add the sliced prime rib to the skillet. Allow to heat through and brown slightly, don’t overcook. Season with Kosher salt and fresh ground pepper.

When browned, add back the caramelized onions to the skillet.

Divide the roast beef and onions into 2 even portions in the skillet. Top each with 3 slices of provolone cheese and turn off the heat allowing the cheese to melt without continuing to cook the beef and onions. You can use a lid if you need to.

One at a time, place the baguette on top of the cheese beef portion and using a spatula, scrap the cheesy beef into the baguette as you turn it over. Repeat with the second baguette.

Serve immediately.