Cook the Potatoes: Boil the russet potatoes in a pot of salted water until fork tender, about 10-15 minutes. Drain and mash them finely until smooth and there are no lumps.

Make the Dough: In a mixing bowl, combine the hot mashed potatoes with salt and potato starch. Gradually knead in warm water until a smooth, pliable dough forms.

Shape the Noodles: Divide the dough into 14 equal pieces. Roll each piece into a rope approximately ½-inch thick.

Cook the Noodles: Bring a large pot of water to a boil. Gently add the noodles and stir until they float to the surface. Boil for an additional minute, then remove and cool them in cold water.

Prepare Chili Oil: In a bowl, whisk together soy sauce, Chinese black vinegar, gochugaru, sugar, salt, minced garlic, and sliced green onion. Heat your neutral oil until smoking and carefully pour it over the mixture, stirring to combine.

Assemble: Drain the cooled noodles and combine them with the garlicky chili oil sauce. Toss well to ensure the noodles are evenly coated, then garnish with roughly chopped cilantro before serving warm.