Boil the potato chunks in a large pot of water until fork-tender (approx. 10-15 min). Drain well.

Transfer the hot potatoes to a mixing bowl. Add salt and mash finely until smooth (no lumps).

While the mashed potato is still hot, mix in the potato starch. Knead gently. Add warm water and continue kneading until a cohesive dough forms.

Divide the dough into equal pieces. On a lightly floured surface (with potato starch), roll each piece into ropes or noodle shapes (approx. ½ inch thickness). Keep unused dough covered with a damp cloth.

In a pot of boiling water, gently add the potato noodles (few at a time) so they are fully submerged. Cook until they float plus about 1 minute. Drain and shock in cold water. Repeat for all noodles.

In a bowl, combine soy sauce, black vinegar, gochugaru, sugar, salt, garlic and green onion.

Heat the oil in a small pan until it just begins to smoke; carefully pour hot oil over the sauce mixture to bloom the aromatics.

Drain the cooked noodles thoroughly and place in a clean bowl. Pour the chili oil sauce over them, then add chopped cilantro. Toss gently until noodles are coated. Serve warm.