Cook the potatoes. Peel and cut potatoes into chunks.
Boil in salted water until very tender, about 12–15 minutes. Drain well and let steam off for 2–3 minutes so excess moisture evaporates.
Mash smoothly. Mash until lump-free. For ultra-smooth noodles, pass through a ricer.
You should have about 2 heaping cups of mashed potato.
Season and cool slightly. Add 1/2 teaspoon salt while the potatoes are warm. Let them cool until just warm to the touch; hot mash will make the dough sticky and hard to handle.
Add starch gradually. Sprinkle in 1 cup potato starch or cornstarch and mix with a spoon, then your hands. The dough should come together into a soft, slightly tacky ball.
If it’s still sticky, add more starch 1 tablespoon at a time. Aim for a dough that holds its shape without cracking.
Divide and shape. Dust your counter lightly with starch. Divide the dough into 4 pieces. Roll each piece into a rope about 1/2 inch (1.25 cm) thick.
For thicker, chewier noodles, go closer to 3/4 inch.
Cut into noodles. Slice ropes into short cylinders (about 1 inch long) for gnocchi-style bites, or keep them as longer strands if you rolled them thinner. Lightly dust to prevent sticking.
Boil briefly. Bring a large pot of salted water to a gentle boil. Add noodles in batches to avoid crowding.
Cook until they float and then 30–60 seconds more. Do not overcook; they’ll turn mushy.
Shock and oil. Use a slotted spoon to transfer cooked noodles to a bowl of cool water to stop cooking, then drain. Toss with a drizzle of neutral oil to keep them from sticking.
Make a quick sauce (optional but recommended). In a skillet, warm 1–2 tablespoons oil or butter. Add minced garlic until fragrant (30 seconds).
Stir in 1–2 tablespoons soy sauce or tamari, a splash of sesame oil, and chili crisp to taste. Add the noodles and toss to coat. Finish with sliced green onions and a squeeze of lemon or a dash of vinegar.
Serve. Enjoy hot as is, or top with sautéed mushrooms, wilted spinach, or pan-seared tofu.
A crack of black pepper or toasted sesame seeds is great for texture.