Salsify gratin is a very common French winter dish that makes use of the root of the salsify plant, which has a flavor reminiscent of oysters. For this version, steamed fingerling potatoes and diced Granny Smith apples make the flavors more interesting, with the acidity of the apples and the starchiness of the potatoes giving the salsify a great balance in both texture and taste. The Mornay sauce for this gratin is made with cheddar cheese, and the crust is topped with rich, nutty Dubliner cheese, which takes this classic French version of comfort food to another level of richness.