• If your roast has a thick layer of fat (fat cap) on top, use a very sharp chef's knife to carefully crosshatch the fat. Liberally season the roast all over with kosher salt, then place it on a roasting pan or rimmed sheet pan and set it in the fridge uncovered for 24 hours. This will allow the salt to penetrate the meat for maximum flavor.
• About 3 ½ to 4 hours before you would like to eat, remove the meat from the fridge and let it sit at room temperature for about 90 minutes.
• While the roast sits, mix the softened butter, garlic, thyme and pepper together. You want the butter mixture to be solid but easily spreadable.
• Preheat the oven to 500˚F with the baking rack set in the middle of the oven. Set the shallots in an even layer in a roasting pan. Set the roast on top and rub the butter mixture all over.
• Roast at 500˚F for about 15 minutes, or until the fat begins to render and brown. Reduce the heat to 325˚F and continue to roast for 14 to 16 minutes per pound, or until the internal temperature of the very center of the roast reaches 125˚F on an instant-read thermometer for medium-rare.
• Remove the roast from the oven, place it on a carving board (you want something that will collect the juices), and tent it with foil. Rest for at least 20 minutes before carving, it will reach 130˚F while resting for med-rare.

For the Au Jus

• If you used a stove-top safe roasting pan, add onion to the drippings (and shallots remaining in the pan, if you made my prime rib recipe) and cook over medium heat for 3–4 minutes, or until the onions start to take on some color.
• Add beef stock and thyme, and bring to a boil. Reduce heat to a simmer and cook until the liquid is reduced by two-thirds, about 20 to 25 minutes.
• Taste the drippings and see if you need additional salt and pepper. Strain through a fine-mesh strainer and transfer to a gravy boat or serving vessel.