Directions

1. Pulse garlic, rosemary, salt, and 1 tsp pepper in a food processor until smooth, then rub all over roast. Transfer to a rack set in a 13- by 9-inch roasting pan and marinate, chilled, at least 8 hours.
2. Let roast stand at room temperature 1 hour.
3. Preheat oven to 450°F with rack in middle. Roast meat, fat side up, 20 minutes. Reduce oven temperature to 350°F and roast until an instant-read thermometer inserted into center of meat (do not touch bone) registers 110°F, 1 1/2 to 2 hours more. Transfer to a platter and let rest, uncovered, 30 minutes (temperature of meat will rise to about 130°F for medium-rare).
4. Do Ahead: Beef can be marinated 1 day ahead.

Cooks' Note To make a roasted garlic garnish that’s as beautiful as it is delicious, halve a few heads crosswise and roast, cut sides down, on a well-oiled sheet of nonstick foil at 350–400°F until caramelized and tender.