Pat the roast completely dry. Rub the kosher salt all over it, set it on a rack over a sheet pan, and refrigerate uncovered overnight, up to two days. The salt seasons deep into the meat and dries the surface so it browns beautifully later.

Take the roast out of the fridge 2 to 3 hours before cooking so it loses its chill. A cold center cooks unevenly. Heat the oven to 250°F (120°C).

Mash the softened butter together with the minced garlic, rosemary, thyme, black pepper, and garlic powder. Smear this herb butter all over the roast.

Set the roast bone-side down in a roasting pan so the bones act as a natural rack. Insert a leave-in thermometer into the thickest part of the center, away from bone.

Roast until the center reads 120°F for medium-rare, about 25 to 30 minutes per pound at this low temperature (roughly 3 to 3.5 hours for an 8-pound roast). Start checking early and trust the thermometer, not the clock.

Pull the roast and tent it loosely with foil. Let it rest 20 to 30 minutes while you crank the oven as high as it goes, 500°F (260°C).

Return the rested roast to the screaming-hot oven for 8 to 10 minutes, until the crust is deep brown and crackly. Keep an eye on it so it does not burn.

Move the roast to a cutting board. Slice against the grain into thick slabs and serve right away, with au jus and horseradish cream on the side.