Attach a deep-frying thermometer to the side of large heavy-bottomed pot or dutch oven, heat 2-inches of oil, over medium-high, to 320 degree F.
Fill a large bowl with cold water. While oil heats, cut potatoes. Using a mandoline fitted with the “waffle” or “crinkle” attachment slice each potato 1/2 inch thick; rotating the potato 90 degrees after each slice to form the waffle pattern. Place slices in water as they’re cut. Rinse potato slices with cold water to remove excess starch. Use paper towels dry potatoes thoroughly. Line two baking sheets with dry paper towels. Working in batches, fry potatoes until they are still pale in color and beginning to soften, about 5 minutes a batch, transfer fried potatoes to towel-lined baking sheets.
Over high, heat oil up to 375 degree F Working in batches, Re-fry potatoes until they are crisp and golden brown, about 2 to 3 minutes. Transfer to towel-lined baking sheets, season with salt. Serve hot.