The Ultimate Prime Rib Recipe: Garlic & Rosemary Rubbed, Drenched

Adjust the oven rack to center position and heat the oven to 250 degrees F (120 degrees C).

Heat a 12-inch oven-proof skillet over medium-high heat. Rub roast on all sides with oil, salt, and pepper. Turn on the exhaust fan, add roast to the hot skillet, and brown it on all sides, about 10 minutes total. Transfer roast to a plate. When cool enough to handle, rub garlic and rosemary all over.

Pour off all but 2 tablespoons of beef drippings. Add mushrooms to the hot skillet and sauté until well browned, about 8 minutes. Mix broth, wine, and mustard; add to mushrooms and simmer to blend flavors and reduce slightly, about 3 minutes. Pour mushroom sauce into a bowl; set aside.

Set a wire rack over the skillet and set roast on the rack. Slow-roast in the oven until roast reaches an internal temperature of 135 degrees F (57 degrees C) for medium-rare. For medium, 140 degrees F (60 degrees C) for medium, about 2 1/2 to 3 hours.

Transfer roast to a cutting board; remove rack from skillet. Pour off excess fat, if any. Set skillet over medium-high heat; return mushroom sauce to pan heat to a simmer. Stir together cornstarch and water in a liquid measuring cup. Add cornstarch slurry and continue to simmer until sauce thickens slightly, about a minute. Carve meat and serve with sauce.