How to roast the garlic: Preheat the oven to 400 degrees F. Cut the top off the garlic and place it on aluminum foil. Drizzle with olive oil and season with salt and pepper. Wrap the foil and bake for 25-30 minutes or until the garlic is tender. Keep it wrapped in foil and set aside.
Let the rib roast rest on the counter for 30 minutes while you roast the garlic. Once the garlic is done roasting, increase the oven to 500 degrees F.
Mix together the softened butter, garlic, thyme, rosemary, salt, and pepper. Thoroughly coat the rib roast with the mixture.
Place a thermometer in the meat, place it in a proper deep dish, and cook for 15 minutes. Reduce heat to 325 degrees. Roast until it’s 5 degrees from your desired temperature. Mine took about 4 1/2 hours. Although I highly recommend checking the temperature at around the 4 1/2 hour mark.
Remove the meat from the oven and wrap it in foil. Let it rest for 20 minutes while you prepare the au jus.
How to make the au jus: Place a skillet over high heat with the pan juices or beef stock (about 2-3 cups) and roasted garlic cloves. Add the wine. Bring to a fast simmer until the liquid has reduced by half.
In a small bowl mix the water and cornstarch. Reduce the heat and add the cornstarch mixture to the pan. Whisk constantly. Wait for it to thicken and season with salt and pepper.
Slice the prime rib and serve with the au jus. Enjoy!