beef tenderloin recipe

4 to 5 lb. Beef tenderloin, trimmed, cut in two pieces and tied. 1 tsp salt 1/2 tsp black pepper 2 tbsp olive oil 4 tbsp butter, salted, softened 2 tsp garlic, minced 1 tsp horseradish, prepared or dijon mustard 1 tsp rosemary, minced or thyme