Preheat the Yoder Smokers YS640s Pellet Grill to 250ºF, set up for smoking, with the second shelf installed.
Trim the hard pellicle of the dry-aged prime rib away, saving for later use. Slather the prime rib roast with a thin layer of Kozlik’s Dijon Classique mustard. Season the roast generously with Jacobsen Salt Co. Black Garlic Sea Salt and fresh cracked Jacobsen Salt Co. Tellicherry Black Peppercorns.
Place the dry-aged prime rib roast on the second shelf of the grill and smoke until the internal temperature reaches 100ºF-105ºF, about two to two and a half hours.
While the prime rib is smoking, prepare the dry-aged beef stock. Dice the reserved pellicle (hard exterior trimmed from the roast) into roughly 1” pieces.
Preheat a Lodge 6 Quart Enameled Dutch Oven over medium heat. Add the diced pellicle to the dutch oven. Cook to brown, about 5 minutes. Add the onions, carrot, fennel, garlic and tomato paste. Cook for a few minutes, stirring. Add the beef stock, fresh herbs, peppercorns and bay leaves. Bring to a simmer. Turn the heat down to low. Cover with a lid and let simmer while the roast is smoking.
When the prime rib roast surpasses 105ºF, remove the roast from the grill and cover with foil. Remove the door from the two-piece diffuser (or the entire diffuser). Place a Lodge Cast Iron Casserole Dish over the fire box and crank the heat up to 500ºF.
Strain the dry aged beef stock through a fine mesh strainer. Discard the solids. Reserve the liquid.
When the grill comes up to temperature (about 10 minutes), sear the prime rib roast in the cast iron casserole pan. Roll to sear on all sides. Remove from the grill when the internal temperature reaches 120ºFº. Cover with foil and let rest while you prepare the beef gravy jus.
Turn the grill temperature down to 400ºF.
Deglaze the casserole dish with the red wine, scraping up the bits stuck to the bottom. Cook until the red wine is nearly entirely reduced out. Add the butter and flour to the dish and stir to form a roux. Cook for about 1-2 minutes.
Add up to one quart of dry-aged beef stock to the roux (start with about half), whisking constantly to remove any lumps. Add the Worcestershire sauce and prepared horseradish. Adjust consistency as needed by adding more stock. Adjust seasoning with salt, as needed.
After resting the prime rib roast for about half an hour, slice to serve. Serve the Dry-Aged Beef Gravy Jus alongside the Dry-Aged Prime Rib.