How to Make It
Preheat the oven to 325°. In a food processor, combine the butter with the garlic, horseradish, thyme, rosemary and sage and process to a paste.
Stand the roast in a very large roasting pan. Season generously all over with salt and pepper and set it fatty side up. Spread the horseradish-herb butter all over the top. Bake for about 3 1/2 hours, until an instant-read thermometer inserted in the center registers 125° for medium rare. Transfer the roast to a carving board to rest for at least 20 minutes or for up to 1 hour before serving.
If making Pat's Popovers, reserve 3 tablespoons of the beef fat from the roasting pan.