Marinate the steaks overnight in the Au Jus. Start a hardwood fire, or get your charcoal burning in a chimney. Place your cooking grate over the fire at a height where the temperature is about 400-450 degrees at the surface (3 second hand count). Place the steaks on the hot grill, turning after about 7-8 minutes. Brush the steaks on the cooked side with the melted butter. When the internal temp reaches the desired level of doneness (130-135 for Medium Rare) remove from the grill and let rest for about 10 minutes Garnish with horseradish and serve