Tourne refers to a vegetable cut to measure 2 inches long with seven sides and tapered at the ends in an elliptical shape. The tourne, which translates from French as "turned" or "to turn," is typically taught in the first classes of culinary school, most often during knife skills or introductory culinary skills classes. Although initially the task of holding a small piece of a vegetable and cutting it into seven equal sides is challenging, it shows your guest you have proficiency and that you take the time and care to finesse your potatoes.
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Peel the potato and square it off by trimming all the sides to flat surfaces. This provides stability and a basic shape to pare down.
Cut the potato in half lengthwise and across the middle. You will have four pieces with flat surfaces, except the sides of the potato that made up the exterior.
Grasp one piece between your thumb and forefinger and taper the edges on both ends. It should resemble the shape of an American football. Repeat with the other pieces.
Grasp the potato between your thumb and forefinger and pare it down to have seven sides, turning the piece in your hand after you pare each side. Repeat with the other pieces.
Square off the ends of each piece. The turned potato should measure between 2 and 2 1/4 inches long.