Preheat oven to 425° F. Arrange oven racks to middle and lower third of oven. Rub all sides of roast with Sazonador and place in roasting pan. Add 2 cups water to pan. Roast on center rack of oven for 30 minutes.
Reduce oven temperature to 350° F. Roast for about 2 ½ hours, until instant read thermometer registers 120° F for medium rare. Remove from oven and let rest 15 minutes before serving. Skim fat from pan juices and discard. Serve pan juices with meat.
Meanwhile, 1 hour before beef is done, place mushrooms in even layer on foil-lined rimmed baking sheet. Bake on lower rack of oven, until mushrooms release liquid, about 25 minutes. Pour off liquid (reserve and add to beef pan juices before serving).
Drizzle olive oil and Sazonador over mushrooms; toss to combine. Return to oven and continue roasting until browned, but still tender, about 15 minutes longer. Add Salsita, vinegar and parsley; toss to combine.
Serve with beef roast and a side of roasted butternut squash. To complete the plate, you may garnish with fresh sage.
1. Plan on 1 pound of bone-in roast per guest; each rib adds 1½ to 2 pounds to the roast. Cooking time is identical regardless of size of roast.
2. Ask the butcher to cut the rib off the bone, and then tie it on with butchers’ twine. This makes for easy carving and eliminates the need for a rack for roasting.
3. To further improve the roast’s crust, allow seasoned roast to air-dry overnight, uncovered, in the refrigerator on a rack before roasting.