When boiled, halved, and with the flesh scooped out (and reserved), potato shells make clever vessels for holding savory fillings and then finishing in the oven. In this recipe, the filling includes tuna cooked with chopped onion, tomato sauce, and the reserved potato flesh. These potato halves are then covered with a luscious bechamel sauce, sprinkled with grated cheese and paprika, and then baked to heat through and crisp up the top, which also becomes wonderfully golden brown.