Let the rib roast rest on the counter at room temperature for 1-3 hours before roasting.
Preheat the oven to 450°F.
Whisk the melted butter, salt, pepper, thyme and lemon zest together. Massage it thoroughly over the entire rib roast.
Lay the roast on the center of a rack in a roasting pan, and roast at 450°F for 20 minutes.
Reduce the temperature to 325°F and roast for 15 minutes for each pound of uncooked roast (so, a 6-pound roast will need 1½ hours). Note: this timing will end in a medium-rare finish; reduce the equation to 14 minutes for each pound for a rare finish.
If you're making the optional creamy horseradish sauce, whisk all ingredients together in a bowl and refrigerate for at least one hour to thicken.
Remove the roast from the oven and let it rest, covered loosely with foil, on the counter for 30 minutes before carving. Then carve, serve, and enjoy!