Perfect Steak Sandwich Recipe | Garlic Butter Steak Seasoning

Ingredients

• Two 6- to 8-ounce steaks, such as culotte, bavette, or flap steak
• 2 tablespoons Garlic Butter Steak seasoning
• 2 tablespoons butter
• 2 large onions, thinly sliced
• 1 tablespoon brown or turbinado sugar
• 1 tablespoon Sherry wine or balsamic vinegar
• ¼ teaspoon Kosher salt and freshly ground black pepper
• 2 tablespoons mayo (preferably Duke’s)
• 1 tablespoon plus 1 teaspoon Creole mustard
• 2 ciabatta rolls (or ciabatta loaf sliced into squares)
• Greens (arugula, leaf or little gem lettuce)