How to Make It
Preheat the oven to 375°. In a spice grinder or mortar, coarsely grind the coriander with the salt and peppercorns. Transfer the spice mixture to a bowl and stir in the olive oil and orange zest to make a paste. Spread the spice paste all over the roast and set it, fat side up, on a rack in a large roasting pan. Pour the orange juice into the pan.
Roast the meat for 25 minutes, then lower the oven temperature to 325° and roast for about 2 hours and 20 minutes longer, or until an instant-read thermometer inserted in the center of the roast registers 125° for rare to medium rare. Transfer the roast to a carving board, cover loosely with foil and let rest for at least 15 minutes before carving into 1/2 -inch-thick slices.