For the creamy horseradish sauce: Place all ingredients into a mixing bowl and whisk together. Cover and refrigerate for at least 4 hrs. (sauce will hold in the refrigerator for up to 1 week). Remove from refrigerator about 20 minutes before serving, adjust seasoning if needed, stir, and serve.
For standing rib roast: Carefully slice fat cap off the top of the roast, leaving the back edge intact (this way you can marinate the beef and then place the fat flap back over the meat before tying with twine). Allow roast to sit at room temperature for about 1 hr.
Place all rub ingredients into a small mixing bowl and whisk together. Generously rub mixture over the entire roast. Replace fat cap back over the top and tightly tie the roast (parallel to the bones) together with cooking twine.
Allow roast to sit for another 30 minutes. At this time, preheat your oven to 500˚F.
Place cut onions, celery and carrots into the bottom of a roasting pan and toss together. Set roast, meat-side up, atop the vegetables and place in the oven.
Roast the beef for about 20 minutes before reducing the heat to 325˚F and continuing to cook your beef for about 11-13 minutes per pound (so about 1 hr. and 30 minutes to 1 hr. and 50 minutes). About ¾ into the cooking time, check the internal temperature of the meat at the thickest part of the beef (make sure the thermometer isn’t hitting the bone. For medium rare, you want the internal temperature to be about 130-135˚F, knowing that when you pull the roast out the carryover cooking will add about another 5˚F) For medium, you want the internal temperature to reach between 140-145˚F.
Loosely cover with foil and allow the roast to sit for about 30 minutes before removing the twine, fat cap and bones, slicing and serving with creamy horseradish sauce and au jus.
For au jus: Once the roast has been removed from the pan, remove and discard the roasting vegetables (they’ll be pretty mushy and stilling in grease at this point, but if you’d like to drain and salvage them for your meal, you totally can! They just need a bit of salt and pepper) and all but 1 tablespoon of grease. Place roasting pan over your stovetop burners and set over medium-low. Add Worcestershire sauce and red wine and reduce by ½. Add the beef stock and reduce by about ⅓. Lightly season with salt and pepper and serve.