Steak and Onion Sandwiches with Horseradish Mayonnaise

• 3 tablespoons butter, divided
• 1 medium red onion, thinly sliced into rounds
• 1 12-ounce rib-eye steak, about 3/4 inch thick
• 1/4 cup mayonnaise
• 2 tablespoons prepared horseradish
• 2 kaiser rolls, halved horizontally, lightly toasted
• 1 cup arugula

1. Melt 2 tablespoons butter in large nonstick skillet over medium heat.
2. Add onion; saute until soft and lightly browned, about 5 minutes.
3. Transfer to plate.
4. Add remaining 1 tablespoon butter to skillet and increase heat to medium-high.
5. Season steak on both sides with salt and pepper.
6. Add to skillet and cook to desired doneness, about 2 minutes per side for medium-rare.
7. Transfer steak to work surface; cover and let stand 5 minutes.
8. Meanwhile, mix mayonnaise and horseradish in small bowl.
9. Spread mixture over cut sides of rolls.
10. Thinly slice steak.
11. Place steak slices on roll bottoms.
12. Top with onions and arugula, then roll tops, and serve.

butter, red onion, mayonnaise, horseradish, kaiser rolls, arugula

Taken from www.epicurious.com/recipes/food/views/steak-and-onion-sandwiches-with-horseradish-mayonnaise-109171 (may not work)