Arrange a rack in center of oven and heat oven to 250º. Put potatoes and 4 cups water into a food processor; pulse until potatoes are cut into roughly ⅛″ pieces. Drain potatoes and rinse, shaking strainer to remove as much water as possible. Transfer potatoes to a tea towel (chop any potato pieces that are larger than ⅛″), cover with another towel, and roll up towels tightly to expel any remaining moisture.
Arrange potatoes evenly on 2 rimmed baking sheets and sprinkle gelatin evenly over potatoes. Bake, rotating baking sheets once, until gelatin melts, about 5 minutes. Transfer potatoes to a large bowl; using a rubber spatula, mix well to distribute the gelatin. Mix in flour and coriander and season lightly with salt. Set a large piece of plastic wrap on a slightly wet work surface (water will help the plastic adhere to the surface) with short end facing you. Place one fourth of potato mixture on plastic wrap, about 6″ from you, and shape into a log about 12″ long and 1″ thick. Lift end of plastic wrap closest to you and bring it over the log, using a ruler to compress roll as you wrap the log. Roll up potato log and set aside. Repeat with remaining 3 batches of potatoes; transfer logs to freezer until firm but not frozen.
Pour oil into a 5-qt. Dutch oven to a depth of 2″ and heat over medium-high heat until a deep-fry thermometer reads 275º. Slice through the plastic to create 1″ by ¾″ Tater Tots; discard plastic wrap. Working in batches, add Tater Tots to oil and cook, turning occasionally, until light brown, about 3 minutes. Using a slotted spoon, transfer potatoes to a rack set inside a baking sheet and chill in freezer for 20 minutes.
Increase oil temperature to 350º. Working in batches, add the potatoes and cook, turning occasionally, until browned and crisp, about 2 minutes. Transfer to paper towels to drain and season with salt. Serve hot.