Prepare Ina Garten's prime rib featured on "Barefoot Contessa" by seasoning a standing rib roast with kosher salt and freshly ground black pepper, then roasting it for about an hour and a half in three separate temperature phases.
Set a three-rib, approximately 8-pound standing rib roast out and allow it to come to room temperature. Set the oven rack to the second lowest position and preheat the oven to 500 degrees Fahrenheit. Place the roast in a large pan bone-side down and evenly distribute 1 tablespoon of kosher salt and 1 1/2 teaspoons of freshly ground black pepper on top.
Roast the meat for 45 minutes at 500 degrees Fahrenheit, then reduce the temperature to 325 degrees Fahrenheit and roast for another 30 minutes. Increase the temperature to 450 degrees Fahrenheit and finish cooking for another 15 to 30 minutes until the internal temperature of the roast reaches 125 degrees Fahrenheit. Remove the roast from the oven, cover tightly with aluminum foil, and allow to rest for 20 minutes.
Create the sauce by whisking together 1 1/2 cups of mayonnaise, 3 tablespoons of Dijon mustard, 1 1/2 tablespoons of whole-grain mustard, 1 tablespoon of prepared horseradish and 1/3 cup of sour cream. Season with 1/4 teaspoon of kosher salt. Carve the roast and serve with the sauce.