Preheat oven to 400°F. Score skin of duck (don’t cut into flesh) with 5 cuts in 1 direction; repeat in opposite direction, making diamond pattern. Sprinkle duck all over with coarse salt, pepper, and ground coriander. Place 2 large ovenproof skillets over medium-high heat. Add duck, skin side down, to skillets, dividing equally. Cook duck until skin is crisp and deep brown, about 7 minutes. Turn duck over; cook 1 minute. Pour off fat. Transfer skillets to oven. Roast duck until cooked to medium-rare, about 5 minutes.