1. Peel the yellow potatoes, chop them into chunks, and boil until tender (a fork easily pierces).
2. Drain and transfer the hot potatoes to a bowl, then mash finely so there are no large chunks.
3. Immediately add the potato starch and water, and mix / knead until you have a firm, smooth dough ball. It helps when the potatoes are still warm.
4. Roll the dough into a long log shape, then cut into 16 pieces (or adjust number depending on how thick you want the noodles to be).
5. Take each piece and roll it into a chopstick-length strip (or your preferred noodle length).
6. Bring a pot of water to boil. Carefully drop the potato noodles in and cook for around 5 minutes or until fully cooked (they may float).
7. Transfer the cooked noodles into cold water, drain them, then place into a serving bowl.
8. Prepare the chili oil sauce: combine garlic, green onion, chilli powder, crushed red pepper, sugar, dark soy sauce, light soy sauce, black vinegar in a heat-proof bowl. Heat the vegetable oil until shimmering and carefully pour the hot oil over the sauce mixture — it will sizzle and release aroma.
9. Pour the sauce over the drained noodles and toss gently so everything is coated.
10. Garnish with roasted sesame seeds and serve immediately while warm.

Note: If your dough is cracking or brittle, it may be too dry — add a few drops of water. If too wet/sticky, add a bit more starch.