Preheat oven to 450F with rack in middle. Rub roast all over with oil, then sprinkle all over with kosher salt. Coarsely crush peppercorns in a folded kitchen towel (not terry cloth with a meat poinder or bottom of a heavy skillet. Coat meat on all sides with peppercorns, pressing to help them adhere.

Roast on a rack in a 13- x 9-inch roasting pan 20 minutes. Reduce oven temperature to 350F and roast until an instant-read thermometer inserted into center of meat (do not touch bone) registers 110F, 1? to 2 hours more. Transfer to platter and let rest, uncovered, 30 minutes (temperature of meat will rise to about 130F for medium-rare).