Classic Steak Sandwich with Caramelized Onions

1.Heat 1 tablespoon of olive oil in a large skillet or Dutch oven over medium-low heat. Add the thinly sliced onions, 1/4 teaspoon of salt, and 1/8 teaspoon of black pepper. Cook, stirring occasionally, for 25-30 minutes, or until the onions are deeply golden brown and caramelized. If they start to stick, add a tablespoon of water to deglaze the pan. Remove from heat and set aside.

2.Pat the sirloin steaks dry with paper towels. Season both sides generously with the remaining 1/4 teaspoon of salt and 1/8 teaspoon of black pepper.

3.Heat the butter in a separate large cast-iron skillet or heavy-bottomed pan over medium-high heat until shimmering. Add the seasoned steaks and sear for 3-4 minutes per side for medium-rare, or longer for desired doneness. Remove steaks from the pan and let them rest on a cutting board for 5-10 minutes.

4.While the steaks are resting, lightly brush the cut sides of the baguettes with olive oil. Place them cut-side down in the same skillet used for the steaks (or a separate pan) over medium heat and toast for 2-3 minutes, until golden brown and slightly crispy.

5.Thinly slice the rested steaks against the grain. Return the sliced steak to the skillet over low heat, if desired, to warm slightly.

6.To assemble the sandwiches, spread Dijon mustard or mayonnaise on the toasted baguettes if using. Layer the bottom half of each baguette with sliced steak, then top with a generous portion of caramelized onions. Place two slices of provolone cheese over the onions.

7.Place the assembled sandwiches (without the top baguette half) under a broiler for 1-2 minutes, or until the cheese is melted and bubbly. Alternatively, place the top baguette half over the cheese and cover the skillet for a minute to melt the cheese.

8.Carefully place the top half of the baguette onto the melted cheese. Slice the large baguettes into individual portions if necessary and serve immediately.