ONE DAY IN ADVANCE - FOR THE RIB ROAST:
Make the rub: Mix the olive oil, parsley, thyme, rosemary, garlic, salt and pepper together in a small bowl until well combined.
Remove the roast from the refrigerator and place, with the fat cap still facing up, on a rack insert in a roasting pan. Allow to sit at room temperature for 1 hour before roasting.
(125 degrees F for medium rare, 135 degrees F for medium, 145 degrees F for medium well)
Remove roasting pan from heat and transfer to a fine mesh strainer set over a saucepan (same pot you used before). Place saucepan over medium high heat and bring to a boil. . Cook until reduced and thickened, about 7 minutes. Taste and adjust for seasoning.
Meanwhile, whisk the heavy cream, mustard, and horseradish in a small bowl. Remove the saucepan from heat and whisk in the cream mixture.
Remove the foil from the roast and return the standing rib roast to the rack insert in roasting pan. Roast until exterior is crisped and browned, about 10 minutes. Remove from oven.
Inactive Time: Overnight in the Refrigerator
*Roasting Technique from Serious Eats