Add the lettuce and tomatoes to the pan and let wilt in the oven for 1 to 2 minutes. Slice the rack of lamb into 4 chops. Spoon some of the potato, lettuce, and tomatoes onto each of 2 dinner plates.

Remove from the heat and keep warm. Carve the duck and serve with the braised lettuce and the potato pancakes. Spoon a little of the cooking liquor from the lettuce over the top and tuck in.