Begin by heating 2 tablespoons of butter or olive oil in a large skillet over medium-low heat. Add the sliced medium yellow onions and season with salt and black pepper. Cook for 30-40 minutes, stirring occasionally, until the onions become a deep golden brown, caramelized, and sweet. In the last 5 minutes, drizzle in 2 teaspoons of balsamic glaze and stir to combine.

While the onions are caramelizing, season your New York Strip steak generously with salt and black pepper on both sides. Heat a heavy skillet over high heat until it’s sizzling hot, then carefully place the steak in the pan. Sear for 2-3 minutes on each side for a juicy medium-rare finish. Once done, remove the steak from the heat and let it rest covered with foil for at least 10 minutes, then slice against the grain.

While the steak rests, take a ciabatta loaf and slice it in half horizontally. Lightly butter or drizzle olive oil on the cut sides. Place each half cut-side down in the same skillet or under a broiler on high, toasting until golden and crispy, about 2-3 minutes. Keep a close eye to avoid burning.

To assemble, spread a generous amount of zesty lemon herb aioli on both toasted ciabatta halves. Layer on the sliced steak, followed by the sweet caramelized onions, and top with a handful of fresh arugula. Close the sandwich and press gently to hold everything together.