1. Pat roast dry with paper towels and place in a large rimmed dish. Using a sharp knife, cut a 1" crosshatch pattern into fat cap (avoid cutting into meat). Rub roast all over with kosher salt and pepper, then cover loosely with plastic and refrigerate for at least 12 hours and up to 1 day. One hour before cooking, remove roast from fridge and place, uncovered, in a roasting rack set in a roasting pan.
2. Center a rack in oven and heat to 250 degrees. Process mushrooms in a food processor until finely ground, about 1 minute. Add garlic and soy sauce and process until very finely chopped, about 1 minute, scraping bowl as needed. Add butter and process until a fine paste forms, about 30 seconds.
3. Rub porcini butter all over beef, then transfer to oven and roast until thickest part of beef registers 130 degrees, 3 to 3 1/2 hours (for best results, begin checking at 2 1/2 hours, then continue to check temperature every half hour). Remove roast from oven, cover loosely with foil, and rest for at least 30 minutes and up to 1 hour.
4. While roast is resting, roughly chop parsley and place in a medium bowl. Zest and juice lemon directly into bowl with parsley, then stir in shallots, thyme, red pepper flakes, oil, and table salt. Let sit at room temperature at least 30 minutes to allow flavors to meld.
5. About 30 minutes before serving, increase oven temperature to 500 degrees. Remove foil, then return beef to oven and roast until exterior is browned and crisp, 5 to 8 minutes. Carve into 3/4"-thick slices and serve with sauce on the side.
Source: Hannaford fresh Magazine, December 2019