Dad's Prime Rib Very easy to make, but make sure to plan about 5 hours from start to table. 8-10 pound prime rib beef roast (bone-in) 1/2 head of garlic, peeled and cloves cut into thirds coarse salt ground black pepper 1 cup Dijon mustard 1. Make 3/4 inch deep slits all over the roast with a sharp paring knife. Insert one garlic slice into each slit. Season entire roast liberally with salt and pepper, rubbing it in. Leave out at room temperature for 1.5 to 2 hours. 2. Preheat the oven to 500°F. 3. After the roast has come to room temp, use a spatula to spread the mustard all over the roast. Place bone side down on a rack in a roasting pan and into oven. 4. Roast for 1 hour at 500°F. Turn off oven, but DO NOT OPEN OVEN DOOR. Leave oven closed, and do not peek for 1.5 hours. 5. Remove from oven and rest for 15 minutes. Check temperature before cutting; the roast should be around 140°F for medium-rare. 6. Cut ribs from roast and slice into 1/2" thick slices. Very good with horseradish cream.