For the sandwich
1 (12-ounce) 1-inch thick boneless New York strip
Freshly ground black pepper
1 large yellow onion, sliced in rings
1/2 teaspoon fresh thyme leaves (or dry if you don’t have fresh)
2 mini focaccia buns, sliced in 1/2
1/2 cup baby arugula
For the Mustard Mayo:
Yield: 1 cup
3/4 cup good mayonnaise
1 tablespoon Dijon mustard
1 tablespoon whole-grain mustard
2 tablespoons sour cream
1/8 teaspoon kosher salt
Whisk the ingredients together in a small bowl.
Season the steak liberally with salt and pepper on both sides. Heat 1 tablespoon of olive oil in a medium sauté pan over high heat until it's almost smoking, then sear the steak on each side for 2 minutes. Reduce the heat to low and cook the steak for about 7 to 10 minutes, turning once, until very rare in the middle, that is if you like it rare.
*Otherwise, after searing on both sides, transfer the steak to an oven safe pan or baking sheet, cover with aluminum foil, and cook for 10 minutes on 350 degrees. That is what I did and it came out perfect and very juicy! Slice the steak into strips.
Using the same sauté pan, heat 1 tablespoon of olive oil over medium heat. Add the onion and thyme and sauté until the onions are brown and caramelized, stirring occasionally. Season with salt and pepper.
To assemble the sandwiches, spread a tablespoon of Mustard Mayo on each bun half. Layer with the baby arugula, steak strips, then with the caramelized onion rings. Cover the sandwiches with the top half of the buns and enjoy!
Source: adapted from Ina Garten