- Purchasing rib roast: For ease in carving, ask your butcher to cut the meat off of the ribs and backbone and tie it back on. Just ask the for a 6-pound rib roast, cut and tied, and they will know exactly what you’re talking about.
- Dry age in the fridge: If you have time, place the roast in the fridge uncovered overnight or for up to 3 days. This allows the outside of the roast to dry out slightly, which intensifies the flavor and gives it a better char. If you don’t have time to do this, it’s ok, seasoning it and cooking it right away will still result in a delicious roast.
- Bring roast to room temp: Take the rib roast out of the fridge 2-3 hours before cooking. Pat it well with a paper towel then cover the whole thing with kosher salt and pepper. Tent it with foil and let it come to room temperature. This is a key tip for even cooking so don’t skip this step.
- Preheat oven to 450°F: Adjust the oven rack to the lower third position so the roast will be sitting in the middle of the oven.
- Prep the pan: Place the garlic halves and onion in the bottom of a heavy bottom, oven-safe skillet, or a roasting pan.
- Garlic herb butter: mix the butter, garlic, and fresh chopped herbs in a medium bowl. Slather the bottom (bone side) of the rib roast with a bit of the butter then place the beef bone side down on top of the garlic and onion. Slather the remaining butter mixture all over the top and sides of the rib roast using a rubber spatula. Insert a probe into the center of your roast if you have one, if not, an instant-read thermometer at the end will work well.
- Quick sear: roast for 20 minutes in the preheated oven.
- Slow roast: when the time is up, reduce the oven temp to 250°F, with the roast still in the oven, and continue to roast for 2 to 2 1/1 hours, or until it reaches 120-125 for medium rare. The time it takes to reach medium rare depends on the exact size and shape of your roast, so go by the temperature of the roast rather than time. Start checking for doneness 30 minutes before.
- Rest: remove the roast from the oven and carefully transfer it to a platter or cutting board to rest for at least 30 minutes.
- Gorgonzola cream sauce: while it’s resting make the gorgonzola cream sauce. Heat a separate clean medium-sized saucepan over medium heat. Add butter and swirl it around to melt. Remove one clove of the roasted garlic from the roasting pan and squeeze the cloves out into the melted butter. Use the back of a spatula to smash the garlic. It should be very soft. Add the chopped shallot and cook until they’re soft and tender. Add the heavy cream and simmer over medium heat until it’s reduced by half, about 10 minutes. Turn the heat to low, add the Gorgonzola and parmesan cheese and stir until it melts. Season to taste with salt and pepper.
- Carve: remove the butcher string and place the bones aside. Slice them into separate ribs and serve those if desired because there is still meat on the bones. Use a sharp chef's knife to slice the rib roast into about 1-inch cuts. You don’t want to slice it too thin.
- Serve: Serve right away with the softened onion and extra roasted garlic from the pan. Drizzle the warm gorgonzola cream sauce on top.
How much prime rib to buy: On average, you should have 3/4 - 1 pound of prime rib per person. Another way to measure it is 2 ribs per person. We purchased a 6-pound (3-bone) rib roast to feed approximately 6 people. I you're serving 4 people, opt for a 4-pound (2-bone) rib roast.
Purchasing the rib roast: call the butcher or meat department of your grocery store a day or two ahead of time and order your prime rib. I called and said "I'd like a 6-pound prime rib roast, cut and tied," and they knew exactly what I wanted. I headed to the store and they had it ready and waiting for me.
Cooking time varies: the cooking time will vary based on the exact size of your roast. It takes approximately 20-25 minutes per pound to cook at 250°F after the quick sear. Start checking the internal temperature early so as not to overcook it.
Pull temp and target temp: pull the roast out of the oven when it reaches an internal temperature 15°F below your target temperature (145°F for medium-rare). Check out this post for determining beef doneness for ideal temperatures.