Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.

Thinly slice chives. Peel and slice onion into ½-inch-thick rounds; separate into rings. Trim and discard root end from lettuce; halve lengthwise. Dice tomato into ¼-inch pieces. Crush croutons in their bag.

In a small bowl, combine mustard, mayonnaise, and half the chives.

In a separate small bowl, whisk together blue cheese dressing, crème fraîche, and 2 TBSP water (4 TBSP for 4 servings).

Pat steak* dry with paper towels; season all over with McCormick Grill Mates Brown Sugar Bourbon Seasoning.

Heat a large drizzle of oil in a large, heavy-bottomed pan over medium-high heat. Add steak and sear, turning occasionally, until browned all over, 3-5 minutes. Turn off heat; transfer steak to a baking sheet.

Roast steak on top rack until cooked to desired doneness, 8-10 minutes. Rinse and wipe out pan.

Once steak is done roasting, transfer to a cutting board and let rest at least 5 minutes.

While steak roasts, in a large bowl, combine tempura batter mix, ⅓ cup cold water (⅔ cup for 4 servings), and salt (we used ½ tsp; 1 tsp for 4). TIP: If mixture seems too thick, add more water 1 TBSP at a time until it reaches a pancake-batter-like consistency.

Add onion to bowl and toss to coat.

Heat a ⅓-inch layer of oil in pan used for steak over medium-high heat.

Once oil is hot enough that a drop of batter sizzles when added to the pan, add coated onion in a single layer (you will need to work in batches!). Cook until golden brown and crispy, 2-3 minutes on the first side and 1-2 minutes on the second side. TIP: Lower heat If onion begins to brown too quickly.

Using a slotted spoon, transfer onion rings to a paper-towel-lined plate. Immediately season with salt.

Halve and toast ciabattas.

Thinly slice steak against the grain.

Arrange steak and as many onion rings as you like on cut sides of half the ciabatta halves. Spread mustard aioli on cut sides of remaining halves; close to form sandwiches.

Divide sandwiches and lettuce wedges between plates. Drizzle dressing over wedges; top with blue cheese, tomato, crushed croutons, and remaining chives. Serve with any remaining onion rings on the side.