Step 2 Arrange potato slices vertically in dish. This is especially helpful for potatoes, zucchini, and squash. Transfer as cut to a bowl of ice and cold water and let chill in water at least 30 minutes. Preparation. Bake 1 1/4 hours. ... Set up the mandoline … To julienne a vegetable means cutting it into thin, uniform matchsticks. Chop the vegetable into chunks that are 2-3 inches (5-8 cm) long. 4. Julienne is a technique that’s used to cut food into matchstick-sized pieces … Add thyme and bake until potatoes … Peel potatoes and cut lengthwise into 1/8-inch-thick julienne in processor or with mandoline. Even though potatoes are round, they can quickly and easily be cut into small, evenly-sized pieces like a julienne. With a sharp knife or mandoline, slice potatoes very thinly crosswise. Wedge shallots throughout. Sprinkle with salt and red-pepper flakes (if using); brush with remaining butter mixture. Advertisement.