Allow the roast to stand at room temperature at least 1 hour before beginning. This will help it cook evenly. You can also season, stuff, and tie the roast a day in advance. Pull it from the refrigerator 1 hour before roasting.
To prepare the roast: Using a sharp knife, remove the chine bone if it is still attached, and then make a slit 3/4 of the way up the fat cap. Pull the fat cap back and season the entire roast with Essence. Place the garlic, thyme and onion slices in-between the meat and fat cap. Lay the fat cap back over the vegetables and meat. Using butchers twine, secure the fat cap to the meat by tying the two together at six different intervals (wrap the twine from the rib end to the loin end). Cover the exposed fat cap with salt and cracked black pepper.
Preheat the oven to 350 degrees F.
Place the roast, rib side down, on a wire rack, set inside a large roasting pan. This will catch all of the drippings from the roast. Place roast in the oven on the center rack. Roast until the internal temperature taken from the center of the roast when measured with an instant read thermometer registers 112 degrees (and no more than 120 degrees)about 2 1/2 to 3 hours for medium rare. While the roast is resting, it's temperature will continue to climb.
Remove the roast from the oven and allow it to rest for at least 45 minutes to 1 hour before slicing. Cut away the butchers twine. Using a sharp knife, carve the roast into individual servings. Reserve the drippings for later use or for Yorkshire Pudding.
Yield: 12 to 16 servings