Ingredients
- 2 medium Vidalia onions, thinly sliced
- 4 tablespoons unsalted butter, divided
- 1/2 teaspoon kosher salt
- 1/4 teaspoon ground black pepper
- 1 1/2 pounds strip steak (about 2 steaks)
- 1 tablespoon Montreal steak seasoning
- 2 small baguettes, halved crosswise
- 1/4 cup whole-grain mustard
- 8 slices fontina cheese
- 2 cups fresh baby arugula
Preparation
Step 1
In a large cast-iron skillet, combine onion, 2 tablespoons butter, salt, and pepper over medium heat. Cook, stirring frequently, until dark golden brown, about 45 minutes.
Preheat oven to 475°. In a large cast-iron skillet, melt remaining 2 tablespoons butter over medium-high heat. Sprinkle both sides of steak with steak seasoning. Add to skillet; cook until browned on both sides, 2 to 3 minutes per side. Remove from skillet; let stand for 10 minutes before slicing.
Place bread on a large rimmed baking sheet. Spread mustard on bottom half of baguettes. Top each with 2 slices fontina. Divide steak and caramelized onions among sandwiches.
Bake until cheese is melted, 5 to 7 minutes. Top with arugula, and cover with top of baguettes.