Prepare Ina Garten’s prime rib from “Barefoot Contessa” by seasoning a standing rib roast with kosher salt and freshly ground black pepper, then roasting it in three consecutive temperature phases for approximately one hour.
Allow a three-rib, about 8-pound standing rib roast to reach room temperature before cooking. Position the oven rack in the second-from-lowest position and preheat the oven to 500 degrees Fahrenheit. Place the roast, bone-side down, in a large skillet and season with 1 tablespoon of kosher salt and 1 1/2 teaspoons of freshly ground black pepper.
Roast the beef at 500 degrees Fahrenheit for 45 minutes, then reduce the temperature to 325 degrees Fahrenheit for an additional 30 minutes. Increase the temperature to 450 degrees Fahrenheit and continue cooking until the internal temperature of the roast reaches 125 degrees Fahrenheit, 15 to 30 minutes longer. Remove the roast from the oven, wrap it securely in aluminium foil, and let it rest for twenty minutes.
Combine 1 1/2 cups of mayonnaise, 3 teaspoons of Dijon mustard, 1 1/2 tablespoons of whole-grain mustard, 1 tablespoon of prepared horseradish, and 1/3 cup of sour cream to make the sauce. Add 1/4 teaspoon of kosher salt to the dish. Carve and serve the roast with the sauce.