1. In the mixing bowl of your KitchenAid, add flour, gluten powder and potato starch. Mix well with a hand whisk. Then fit KitchenAid with the dough hook.
2. In a small cup, add salt and water. Mix well until dissolved.
3. Slowly drizzle in water mix, scraping down the sides of the bowl as needed while you mix at the lowest speed. Continue until the dough comes together into a shaggy dough.
4. Transfer the dough out to the work surface and knead by hand. Shape it into a rough ball. Cover with plastic wrap and let it sit for about 1 hour.
5. Divide into 3 equal pieces on the work surface. Cover with plastic wrap. It is OK if the dough is not smooth at this stage.
6. Fit the Pasta Roller onto the KitchenAid mixer. Set it to position 1 (thickest). Flatten by hand one dough piece into a rough rectangle about 1.5 cm thick. Process at speed 1 and slowly feed the piece of dough through the Roller. Feed it through again at the same (thickest) setting 1 several times until the dough is silky and smooth. You may fold it in half before running it through. It usually takes me about 10 times and sometimes more. In the beginning the dough will be ragged. As you repeat, after more runs, it will get silky and smooth alright.
7. Once the dough is smooth, turn the dial to the next thickness setting 2 and run the dough through once or twice.
8. Repeat #6 and #7 with the rest of dough balls.
9. Attach the Spaghetti Cutter and run the dough through to cut it. Dust generously the noodles to coat them with potato starch and gently shape into serving sized bundles. Place on the prepared plate. Repeat with the remaining dough pieces.
NOTE: you can also cut by hand. Check out the video below!
10. Get a large pot of water boiling. Add the noodles to boil there for 10min. Now you can stir them gently but only at the very beginning. It is better not to touch the udon after that, or they might become very fragile and break down into short bits. Strain and rinse the udon noodles with running water to remove the gooey texture from the surface. Immerse the washed udon back in boiling water to warm them up. Pull them out again of the water, serve in a bowl before pouring the hot soup.
You can enjoy the cold udon, directly after the cold water rinsing with tsuyu!