Ingredients
- 1 (12-ounce) 1-inch thick New York strip boneless beef top loin steak
 - Montreal Steak Seasoning
 - Salt and pepper
 - Olive oil
 - 2 yellow onions, sliced in rings
 - 1/2 teaspoon fresh thyme leaves
 - Mustard Mayo, recipe below
 - 2 small ciabatta buns
 - 1/2 cup arugula
 - 1 tomato, sliced
 
Mustard Mayo:
- 1/3 cup good mayonnaise
 - 2 tablespoons Dijon mustard
 - 1 tablespoon whole-grain mustard
 - 2 tablespoons sour cream
 - 1/8 teaspoon kosher salt
 
Whisk the ingredients together in a small bowl and set aside until assembling sandwiches.
Directions
- Season the steak liberally with Montreal Steak Seasoning, salt, and pepper on both sides.
 - Heat 1 tablespoon of olive oil in a medium saute 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 for about 7 to 10 minutes, turning once, until very rare in the middle.
 - Remove to a plate, cover tightly with aluminum foil, and allow to sit for 10 minutes. Slice the steak into strips.
 - Using the same saute 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 brown and caramelized, stirring occasionally.
 - To assemble the sandwiches, spread a tablespoon of Mustard Mayo on the bottom half of each bun.
 - Layer the steak strips on top of the mayo, sprinkle with salt and pepper, and top with the caramelized onion rings.
 - Place the arugula and sliced tomato on top of the onion rings, and cover the sandwiches with the top half of the buns.
 
Recipe from Smitten Kitchen.