Preheat the oven to 450 degrees. Take the roast out of the fridge 15 to 20 minutes before starting to prep the roast.
Make the spice rub paste combine the garlic powder, salt, cumin, cinnamon and paprika in a bowl. Stir in 2 tablespoons of the olive oil to form a paste.
Place the roast on a work surface, rib bone side down. Spread most of the spice paste over the top of the roast, and work a little into the side and bottom.
Move the the roast to a rack on in a roasting pan. Place the roasting pan in the preheated oven.
Sear on 450 degrees for 15 minutes. Drop the heat to 325 degrees, and roast for approximately 2 hours 15 minutes. That was the time given by the Certified Angus Beef® Brand Roast Perfect App. Times will vary a bit based on the oven and meat quantity. Use a meat thermometer to check for doneness. 135 degrees is medium rate. When done, remove beef from oven and let rest on platter for at least 10 minutes. Reserve the meat juice that has built up in bottom of pan.
With about 1/2 hour left in the roasting time, heat the remaining tablespoon olive oil in a skillet on medium high. Stir in the onions with a pinch of salt. Cook on medium high for 5 to 10 minutes, stirring infrequently so that the onions will brown.
When the onions have begun to brown nicely, add the butter to the skillet and lower heat to medium low. Cook for another 10 minutes until the onions are very soft and brown. Keep on low heat until the meat is done.
Pour the meat juice from the roasting pan in with the onions increase heat to simmer for a few minutes, stirring occasionally. Move the onions to a serving bowl.
Slice the beef, and plate, topped with a bit of the caramelized onion mixture. Enjoy!