Ingredients: 1 (12- ounce) 1- inch thick steak,Kosher salt,Freshly ground black pepper,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,1/2 cup baby arugula
- 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.
- Using the same pan, heat 1 1/2 tablespoons of olive oil over medium heat.
- Add the onion and thyme and saute for 10 minutes, until the onions are caramelized, stirring occasionally.
- Whisk mayo, mustards, sour cream, and salt into a bowl and set aside.
- 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.