|4-5 lb Prime rib roast|
|2 1/2 tbsp Olive oil|
|1 tbsp Kosher salt|
|1 tbsp Freshly ground black pepper|
|2 tsp Chopped fresh thyme|
|2 tsp Garlic powder|
Set an oven rack to the lowest position and preheat the oven to 400 degrees F.
Cut the onions into eighths lengthwise and place in a roasting pan just large enough to fit the prime rib. Drizzle the onions with 1 tablespoon of olive oil and toss to coat evenly.
Secure the outer layer of meat on the prime rib by tying pieces of twine parallel to and between the ribs; this will ensure even cooking. Drizzle 1 tablespoon of olive oil over the rib roast and rub the whole surface to coat evenly. Sprinkle the kosher salt, pepper, thyme, and garlic powder evenly on all sides.
Heat a large sauté pan with the remaining ˝ tablespoon of olive oil over medium-high heat. Add the prime rib and cook all sides of the meaty part until golden brown, about 2 minutes per side. Place the prime rib in the prepared roasting pan on top of the onions. Set the prime rib aside until cooled to room temperature. (This will help ensure even cooking.) Once it has reached room temperature, place in the oven and cook for 15 minutes. Reduce the oven temperature to 325 degrees F, and cook until it reaches a temperature of 115 degrees F for medium-rare, about 45 minutes longer. Remove from the oven, tent with a piece of aluminum foil, and let it rest for 20 to 30 minutes; the cooking will carry-over and the temperature will continue to rise. When cool enough to handle, slice meat from the ribs and cut into slices across the grain.