To roast garlic...
1. Cut whole bulb of garlic in half, width wise.
2. Drizzle with olive oil.
3. Season with salt and pepper.
4. Wrap with tin foil
5. Bake at 350*F for 1hr to 1.5hrs (or with prime rib roast).
Use as desired. Goes great in mashed potatoes.
To make sauce...
6. Mash roasted garlic in bowl.
7. Add sour cream and mix well.
8. (Optional) Add horseradish to taste.
9. Season with salt and pepper.
Serve next to prime rib.