Steak and fried onion sandwiches

Ingredients:

• 3 tablespoons unsalted butter, room temperature
• 2 onions, thinly sliced
• 1 tbsp + 2 tsp Worcestershire sauce
• 3/4 cup grated white cheddar
• 3 tablespoons ketchup
• 2 tbsp mustard
• 1 tbsp steak sauce
• 1 tbsp. mayonnaise
• 700 gr. skirt steak, cut into 4 pieces
• 4 thick slices sourdough bread with crust
• 1 bunch watercress, ends trimmed

Preparation:

1. In a large saucepan over medium heat, melt 2 tablespoons butter. Add the onion, 2 tablespoons water, and a large pinch of salt. Cook, stirring occasionally and adding up to 1 tablespoon more water if needed, until the onion is caramelized, 15 to 20 minutes. Add another 2 tablespoons water and 1 tablespoon Worcestershire sauce. Gradually add the cheese, stirring until melted. Cover and keep warm.
2. Meanwhile, in a small bowl, combine the ketchup, mustard, steak sauce, mayonnaise, the remaining 2 tablespoons Worcestershire sauce, and a few freshly ground black peppers.
3. Heat a large cast-iron skillet over high heat. Season the steak generously with salt and pepper. Add to the skillet and cook until browned, about 3 minutes per side for medium-rare. Transfer the steak to a cutting board and let rest for 5 minutes.
4. Toast the bread and brush with the remaining 1 tablespoon butter; divide among plates. Thinly slice the steak and place on the bread. Drizzle with the sauce, reserving 2 tablespoons for the salad, and top with caramelized onions.
5. Mix the remaining sauce with the watercress, season with salt and pepper to taste. Serve with sandwiches.