1. Hand whisk together bread flour and plain flour in your stand mixer bowl. Fit it with the dough hook.
2. In a small cup, add salt and baking soda. Mix well until dissolved, then add egg yolk. Mix well.
3. Slowly drizzle in water, scraping down the sides of the bowl as needed, mix at the lowest speed until the dough comes together into a shaggy dough.
4. Transfer the dough out to a floured 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 pieces on the work surface. Cover loosely with plastic wrap. Do not worry 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 one piece of dough through the Roller. Feed it through again at the thickest setting 1 several times until the dough is silky and smooth. You may fold it in half before running it through. It takes me about 10 times or more usually. In the beginning the dough will be ragged. As you continue, after more runs, it will get silky and smooth alright.
7. Once the dough is smooth, turn dial to the next setting 2 and run dough through once or twice. Repeat (once or twice) at each following position until you reach setting 5 or 6.
8. Repeat with the rest of dough balls.
9. Now attach the Spaghetti Cutter and run dough through to cut. Dust generously the noodles with katakuriko/potato starch to coat and gently shape into serving sized bundles. Place on the prepared plate. Repeat with the remaining dough pieces.
10. Cover with plastic wrap and let it sit in the fridge for 1~2 days. Well, you can skip this step if you want to use them on the same day.
11. Start boiling a large pot of water. Boil the noodles for 2~3min until you get the texture you like. Serve with hot soup!
TIP: You can also freeze the noodle bundles to use them later.