1. Preheat oven to 425°F. Combine salt and pepper; coat roast evenly with seasoning on all sides. Arrange garlic in bottom of roasting pan; place roast over garlic, bone-side down, making sure to cover garlic completely with roast. Bake 20 minutes or until browned.
2. Reduce oven to 350°F; cook 1–1 ½ hours and until roast is 125°F (for medium rare; warm red center), 130°F (medium; warm pink center), or up to 170°F (well done). Use a meat thermometer to accurately ensure doneness. Transfer roast to cutting board; let stand 10–15 minutes before slicing. Temperature will rise 5–10°F during this time.
3. Transfer roasted garlic to 2-quart stockpot; smash cloves into a paste. Add cream, broth, and thyme to garlic; simmer 10–12 minutes or until liquid is reduced by one-half. Remove thyme and stir in vinegar. Slice roast; serve with sauce on the side.

NOTE: The doneness temperatures for medium rare and medium stated above are traditional temperatures used for cooking rib roast, but are not recommended by the USDA. To maintain food safety, the USDA recommends an internal temperature of 145°F, as measured using a food thermometer, with a 3-minute rest time before carving.