For ease in carving, ask your butcher to cut the meat off of the ribs and chine (backbone) and tie it back on.
The day before you plan to roast your prime rib, season it liberally on all sides with salt and pepper. Place the roast on a heavy baking sheet with the fat cap side up and refrigerate, uncovered, overnight (or up to 24 hours).
Remove the prime rib from the refrigerator and let stand at room temperature for 2 hours before roasting.
Preheat oven to 250°F with the rack in the lower third of the oven. Place prime rib on a v-rack in a roasting pan with the fat-cap side up.
Roast until an instant-read thermometer inserted into the thickest part of the meat (away from the bone) reads 120-125°F for rare, 128-130°F for medium-rare, or 132-135°F for medium and medium-well. This will take 3-4 hours.
Remove the prime rib from the oven, tent with foil, and let rest for 30 minutes.
Increase oven temperature to 500°F. Uncover the roast and sear it in the oven for 5-10 minutes, until the exterior is brown with a crisp crust.
Carve the prime rib and serve with Roasted Garlic Horseradish Cream Sauce on the side.
