The Best Steak Sandwich
2 1/2 tablespoons Olive oil
2 yellow onions, sliced in rings
1/2 teaspoon fresh thyme leaves
3/4 cup good mayonnaise
1 tablespoon Dijon mustard
1 tablespoon whole-grain mustard
2 tablespoons sour cream
1/8 teaspoon salt
4 sub rolls
Season the steak with salt and pepper on both sides. Heat 1 tablespoon of olive oil in a pan over high heat until it's almost smoking, then sear the steak on each side for 1 minute. Reduce the heat to low and cook the steak until desired doneness. Remove from heat and let sit for 10 minutes. Slice the steak into strips.
To assemble the sandwiches, spread a tablespoon of mayo sauce on each side of the roll.Place a layer the steak strips on top of the mayo, sprinkle with salt and pepper, and top with the caramelized onion rings. Place the baby arugula on top of the onion rings, and cover the sandwiches with the top half of the buns.