1⁄4 cup mayonnaise
2 tablespoons prepared white horseradish
2 tablespoons (1⁄4 stick) butter, divided
3 – 1-inch-thick beef tenderloin steaks
Salt and Pepper, to taste
11⁄2 medium onions, thinly sliced
4-6 ounces large shiitake mushrooms, stemmed; Caps thinly sliced (about 21⁄2 cups) 1⁄2 cup beef broth
4 slider buns, halved horizontally
1 cup arugula
6-8 ounces brie cheese
Mix mayonnaise and horseradish in small bowl to blend.
Melt 1 tablespoon butter in large, heavy skillet over medium-high heat. Sprinkle tenderloin steaks with salt and pepper. Add steaks to grill and cook to desired doneness (about 5 minutes per side for medium-rare). Using tongs, transfer steaks to work surface. Leave brie at room temperature for later use.
Melt 1 tablespoon butter in skillet over medium-high heat. Add onions; sauté until dark brown (about 25 minutes). Add mushrooms; sauté until tender (about 5 minutes). Add broth; boil until juices are reduced to glaze, stirring occasionally (about 1 minute). Season onion mixture to taste with salt and pepper.
Place slider bottoms on plate and spread each with horseradish mayonnaise. Place arugula leaves on slider tops. Thinly slice steaks, and divide evenly among sliders. Top with brie cheese and then onion mixture. Spread remaining mayonnaise on cut-side of slider tops. Place tops on sandwiches.
Recipe by Chef Day