For the beef tenderloin:
1 (2 1/2 to 3 pound) beef tenderloin, preferably the center cut
2 to 3 teaspoons kosher salt
1 to 2 teaspoons freshly ground black pepper
3 tablespoons unsalted butter, melted
For the horseradish sauce:
1/2 cup mayonnaise, store-bought or homemade
1 tablespoon prepared horseradish, or to taste
2 tablespoons whole or 2% milk
Freshly ground black pepper
For the sliders:
Dinner rolls, such as Parker House
Spinach or arugula
Whole grain mustard
Remove tenderloin from the refrigerator at least one hour before cooking. Trim any fat and silver skin from the beef and discard.
Preheat the oven to 475°F. Tie the roast in 1 1/2-inch intervals if necessary and place in a large roasting pan. Season with salt and pepper. Cook the beef for 15 minutes. Pour the butter over the beef and continue roasting until it reaches an internal temperature of 130°F for medium rare, 25 to 30 minutes. (The temperature will rise 5 to 10 degrees while resting.)
Allow the meat to cool to room temperature, then wrap in foil and refrigerate for 8 hours or overnight. Cut into very thin slices for sliders.
For the horseradish sauce, combine mayonnaise, horseradish, and milk until desired consistency is reached. Season with black pepper.
Serve sliced beef with dinner rolls, spinach, and horseradish sauce.