1Combine the rub ingredients in a small mixing bowl, then rub mixture into the beef roast.
2Let the roast sit out for 30 minutes to become room temperature and allow the rub to seep in.
3Preheat your oven to 500°F.
4Heat a cast iron pot or skillet over medium-high heat with olive oil, then sear the meat 2 minutes per side until all sides are seared.
5Place the roast in the oven uncovered, closing the oven door and turning off the heat; leave the meat in the oven until it comes to 125°F. This might take an hour or up to three, depending on the size of roast you select.
6Remove the roast and allow it to rest for 20 minutes.
7Heat the skillet that roasted the beef over medium-high heat and add in the chopped onion, stirring to scrape up the beef drippings.
8Once the onions are soft, add in Worcestershire sauce, cranberry sauce and Coca-Cola, and bring to a simmer, allowing it to bubble away, reducing over 20 to 30 minutes while your meat finishes resting.
9To complete the sauce, using a blender, blend the sauce until smooth and season with salt to taste. Let that keep simmering on low until you're ready to serve.
10Finally, slice up your roast into 1/2-inch thick slices and serve with the sauce.