How to Make It
Stir together butter, salt, mustard, pepper, and garlic. Place beef on a wire rack in a rimmed baking sheet. Rub butter mixture all over beef, and chill, uncovered, at least 8 hours.
Let beef stand about 20 minutes at room temperature. Preheat oven to 425°F. Bake in preheated oven until a meat thermometer inserted into thickest portion registers 135°F (medium-rare), 25 to 30 minutes. Cover loosely with aluminum foil; let rest about 15 minutes before slicing.