1. In your stand mixer's bowl, add buckwheat flour, bread flour and gluten. Mix with a egg whisk. Then fit the KitchenAid with its dough hook.
2. Slowly drizzle in the water, scraping down the sides of the bowl as needed while you mix at the lowest speed. Continue until it comes together into a shaggy dough.
3. Knead the dough by hand (as is, in the bowl) for a few minutes. Then transfer it out to your work surface and shape it into a rough ball. Cover with plastic wrap and let it sit for about 1 hour.
4. Divide into 6 equal pieces on the work surface. Cover with plastic wrap. It is OK if the dough is not smooth at this stage.
5. Fit the Pasta Roller on 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. In the beginning the dough will be ragged. As you repeat, after more runs, it will get silky and smooth alright.
6. Once the dough is smooth, turn the dial to the next thickness setting 2 and run the dough through once, then setting 3. Dust with corn starch and set is aside.
7. Repeat #5 and #6 with the rest of dough balls.
8. 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.
How to boil
Get a large pot of water boiling. Add the noodles to boil there for about 30 seconds or more. You can stir them gently but only at the very beginning. It is better not to touch the soba after that, or they might become very fragile and break down into short bits. Once the soba rise in the water then strain. Rinse in cold water gently to remove the gooey texture from the surface. Immerse the washed soba back in boiling water to warm them up (at least if you are going to eat it hot). Pull them out again of the hot water, and serve in a bowl before pouring the hot soup on them.
NOTE: Better boil the soba a small quantity at a time to avoid cutting them.
You can also enjoy cold udon, directly after the cold water rinsing with tsuyu.