Dry and salt the roast. Pat the boneless prime rib very dry with paper towels. Sprinkle the kosher salt evenly all over the roast, pressing it on so it sticks. (This helps the seasoning actually reach the meat, especially if you do the optional dry brine.) Place the roast on a wire rack set in a rimmed baking sheet or roasting pan.

Optional but excellent: chill uncovered. If you have time, refrigerate the salted roast uncovered for 8 to 24 hours. This acts like a dry brine and helps the surface dry out for a better crust. If you are cooking right away, no worries. Keep going.
Make the butter rub. In a small bowl, mix the softened butter, olive oil, garlic, rosemary, thyme, pepper, and Dijon (if using).
Rub and heat the oven low. Rub the butter mixture all over the roast. (No extra pepper needed, it is already in the rub.) Set the oven to 250°F. If the roast is fridge-cold, letting it sit out for about 30 minutes while the oven heats is fine, but do not leave it out longer than 2 hours total.

Slow roast to pull temperature. Insert a probe thermometer into the center of the thickest part, not touching the rack or pan and not sitting in a fat pocket. Roast until the internal temperature hits these pull temps (before the high-heat finish):
- 120°F for rare
- 125°F for medium-rare
- 130°F for medium
- 135°F for medium-well
For a 4 to 5 pound roast, this often takes about 2 to 2 1/2 hours, but go by temperature, not the clock.
Heads up: It will rise about 5 to 10 degrees during the rest and finish.

Rest, then crank the heat. Remove the roast and rest it uncovered for 30 minutes (this keeps the surface drier for a better crust). If your kitchen is cold and you are worried about it, you can tent it very loosely with foil, but keep it breezy. During the rest, raise the oven to 500°F (or as high as your oven safely goes, 475°F to 500°F is great). Turn on your vent or crack a window if your oven tends to get smoky.
Finish with a hot sear. Return the rested roast to the hot oven and roast 6 to 10 minutes until the exterior is deeply browned and crisp. Watch closely at the end. This part moves fast.
If 500°F is too smoky: Broil on high for 2 to 5 minutes, rotating once for even browning.

Final rest and slice. Rest the roast 10 to 15 minutes. Remove twine or netting. For easier carving, set the roast so the cut face is stable, then slice across the grain into 1/2-inch slices for classic prime rib, or thinner if you are going sandwich mode.

Quick pan sauce (optional but recommended). Pour any drippings from the roasting pan directly into a small saucepan. (Do not put a rimmed baking sheet on the stove, it can warp.) Add beef broth and Worcestershire, scraping up any browned bits from the pan first if you used a sturdy roasting pan. Simmer 3 to 5 minutes.
If there are not many drippings, do not stress. The broth and Worcestershire still make a tasty quick au jus.
For a slightly thicker sauce, whisk in the cornstarch slurry and simmer 30 to 60 seconds. For an extra-nice finish, whisk in a small knob of butter off heat. Taste and adjust salt and pepper.
Serve. Spoon pan sauce over slices, add a pinch of flaky salt if you are feeling fancy, and bring it to the table like you totally do this every week.
