Perfect Prime Rib With Creamy Horseradish Sauce

This is how my husband prepares a rib roast. I do not know where the recipe came from. I just can never find the directions, so thought I would post it here and share.

• Ready In: 4 hrs 15 mins
• Serves: 4

Ingredients

• 5 -6  lbs  prime rib roast, room temperature
• 1  tablespoon salt
• 1⁄2 tablespoon pepper
• 1  tablespoon garlic powder
• 1  tablespoon rosemary
• 1⁄4 cup mayonnaise
• 1⁄4 cup sour cream
• 1 -2  tablespoon  prepared horseradish (to taste)
• 1 -2  green onion, finely chopped

Directions

1. Preheat oven to 375 degrees. Mix together Salt, Pepper, Garlic Powder and Rosemary. Rub roast all over with dry rub. Place roast on rack in middle of oven. Roast 1 hour. Turn oven off. Do not open oven at any time. May be held in oven for several hours. Turn oven on again to 375 degrees for 30 minutes before serving for rare, 40 minutes for medium rare. Works for any size prime rib roast.
2. While cooking mix together, Mayo, Sour Cream, Horseradish, and Ground Onion. Chill and serve with dinner.