1 (1-inch-thick) sirloin steak (1 1/2 to 2 lb)
3/4 teaspoon salt
3/4 teaspoon black pepper
1/2 cup sour cream
2 tablespoons drained bottled horseradish

Preheat broiler.
Oil rack of a broiler pan.
Pat steak dry and sprinkle all over with 1/2 teaspoon salt and 1/2 teaspoon pepper.

Broil steak on rack of broiler pan 3 inches from heat 4 to 5 minutes per side for medium-rare. Transfer to a cutting board and let stand, loosely covered with foil, 5 minutes.

Stir together sour cream, horseradish, and remaining 1/4 teaspoon salt and 1/4 teaspoon pepper in a small bowl and serve with steak.