Season the roast generously with salt and pepper and let sit in the refrigerator, uncovered, overnight or as long as you can even if its just 30 minutes - this will make for a crustier crust but if you have no time to spare, don't panic, just season the meat and move on to the next step.
Preheat the oven to 250˚F and place the roast, with fat cap up, on a v-rack set in a large roasting pan, or on a wire rack set in a rimmed baking sheet.
Cook until the center of the roast registers 130-135°F on an instant-read thermometer. This will take 3½ to 4 hours so I like to start checking the temperature after 3 hours.
Remove the roast from the oven, tent loosely with foil and let rest at least 30 minutes and up to 2hrs.
Turn the oven up to 500˚F - and get any sides, veggies, drinks etc ready while the oven heats up.
Put the roast back in the oven and cook until the outside is a crispy dark golden brown, about 10 minutes.
Carve and serve immediately.**
Notes
*plan on ¾ lb per person of bone-in prime rib which is about 1 rib for 3 people. Your regular grocery store butcher should be able to give you the exact cut you need. To make it even easier on yourself, ask them to cut out the ribs and tie them back in place so when it comes time to carve you dont have to worry about cutting around the ribs or removing them yourself. **This recipe works for roasts of any size - of course the cook time may vary slightly but the target temperature remains the same. This makes the most delicious leftovers for a steak sandwich or steak and eggs so I would recommend making a little more than necessary.
Recipe by Eat Some Wear Some at https://eatsomewearsome.com/slow-cooked-prime-rib-roast/