Duchess potatoes are an elegant, French-pedigreed classic in which mashed potatoes are enriched with egg, piped into decorative rosettes, and baked until golden brown. The egg lightens the potato, creating an almost weightless, dainty fluff that contrasts with the crispy, craggy exterior. In 1867, an article in Galaxy magazine lamenting the state of American cooking noted duchess potatoes on the menu of a rare good dinner. For the next century, the dish made regular appearances on the menus of country clubs, ocean liners, and fancy-pants restaurants, but by the 1970s, it seemed stuffy and out of step with the times, and it fell into culinary disrepute. Which is a shame, because duchess potatoes really are something very special.
We transformed the regular hands-on skillet method to a very hands-off oven technique.
Be prepared to fry the potatoes twice: once to cook them so they fluff inside and again to get them crispy on the outside. When I use an electric fryer, I always follow the manufacturer's instructions. To make good fries in a pot on the stove, a deep-fat thermometer is essential. It ensures that the oil is at the proper temperature for deep-frying and lets you check that the oil isn't overheating, a potentially dangerous situation. A mandoline is a very useful slicing tool for cutting the potatoes (and other vegetables) quickly and to a uniform size. Both the deep-fat thermometer (also called a candy thermometer) and the mandoline are available at most cookware stores. The third essential is a pot that is large and tall enough to contain the oil without overflowing when the potatoes are slipped in.
We came up with this soup years ago simply by using two things we always have plenty of at Thanksgiving: turkey stock and leftover mashed potatoes. Now we make even this when we don’t have leftover potatoes. This soup is quite delicate and soothing after all the Thanksgiving gluttony.