Before you begin: Remove the roast from the refrigerator 2+ hours before roasting.
Remove any packaging and pat the meat dry with a paper towel. Place the beef, ribs-side down, on a baking sheet fitted with a wire rack, so it doesn’t sit it any juices that may leach out.
Combine the flour, salt, and pepper in a small bowl and sprinkle it over the top and sides of the roast, patting it down to help it adhere.
Let the roast sit on the kitchen counter uncovered for 2+ hours to bring it to room temperature (this gives you a better crust and more even cooking).
Position the oven rack ahead of time, so the roast will sit centered in the oven. Preheat oven to 450°F.
Place the beef in the Dutch oven, ribs-side down, and insert the meat thermometer into the thickest part of the meat away from the bone.
Roast uncovered for 20 minutes, or until the top is nicely browned and beginning to crust.
Reduce oven to 225°F and continue roasting uncovered until the meat registers an internal temperature of 120°F (about 2 hours)
Remove the roast from the oven, and let it sit undisturbed in the Dutch oven for 10 minutes to lock in the juices.
Transfer the roast to a cutting board while you prepare the au jus.
Remove all but ½ cup of the fat from the Dutch oven. Over medium heat, sprinkle flour onto the remaining pan drippings, scraping them up and whisking until combined. Let it cook for 2 minutes, or until the mixture begins to foam and deepen in color.
Little by little, whisk in the broth until combined and smooth. Increase heat to high and bring the mixture to a boil, stirring continuously until only slightly thickened.
Strain through a fine mesh sieve and season to taste with additional salt and/or pepper if desired.
The roast should now have an internal temperature of 125°F for medium-rare. If not, tent it with aluminum foil to bring it up to desired temperature.
Cut away the twine (if any) and the rib section in one piece. Then Carve the roast into slices as thick or thin as prefer, and serve with the au jus.