Before cooking, remove the prime rib from the refrigerator 1 hour before you plan to cook it. Once it is at room temperature, season it on both sides with salt.
Adjust your oven rack so that the prime rib will roast in the middle of the oven when you are ready to cook it. Preheat the oven to 500 degrees Fahrenheit.
Mix the salt with the pepper, rosemary, thyme, garlic, and olive oil.
Pat the roast with paper towels. Rub both sides of the roast with the herb mixture. If cooking a bone-in roast, place the roast in a cast iron roasting pan with the bones facing down. Meanwhile, if you are cooking a boneless roast, place it on a rack within the pan.
Bake the prime rib for 15 minutes. Then, lower the oven temperature to 325 degrees Fahrenheit and bake until it is cooked to your desired doneness.
Rare: Cook until the thermometer registers 120 degrees Fahrenheit (about 10 to 12 minutes per pound).
Medium rare: Cook until the thermometer registers 130 degrees Fahrenheit (about 13 to 14 minutes per pound).
Medium: Cook until the thermometer registers 140 degrees Fahrenheit (about 14 to 15 minutes per pound).
Medium Well: Cook until the thermometer registers 150 degrees Fahrenheit.
Here are a couple of things to keep in mind:
A meat thermometer is vital for achieving the desired doneness, as not every roast or oven is the same.
In addition, the meat will continue to cook after being removed from the oven (your thermometer will continue to climb 5 to 10 degrees), so remove it 5 to 10 degrees before it reaches the desired temperature.
Take it out of the oven and tent it with aluminum foil. Before carving, let it rest for 30 minutes.
Carve your roast by slicing it against the grain at a thickness of about a 1/2 inch. If desired, serve with horseradish.