Put the bread flour and all-purpose flour into a large bowl and mix well. In a different bowl, add the egg, salt, water, and baking soda. Stir well until the salt dissolves.

Create a well in the middle of the flour, pour in the salt water prepared in Step 1 and mix well using your hands.

It will be very dry and hard to mix at first, but keep kneading patiently and try not to add more water.

When the dough comes together, put it in a large plastic or Ziploc bag, seal and step on it with your feet to knead the dough. (When the dough flattens out, fold it into quarters and step on it again.)

Repeat the stepping and folding process 3 times, and leave the dough to rest for 2-5 hours.

If you have a pasta machine, set the dial to 4 or 5, and cut the dough into thin noodles. If you don't have a pasta machine, roll the dough out with a rolling pin to about 2 mm thick, and slice into 2 mm noodles.

Dust the noodles evenly with cornstarch (or katakuriko) to prevent the noodles from sticking to each other.

If you divide the noodles into 150 to 160 g portions, you'll have exactly 5 servings. If you prefer rippled noodles, squeeze the noodles well.

Boil the noodles in plenty of boiling water, taking care not to let it boil over, for 1.5 minutes. Noodles containing baking soda will make the water boil over, so be careful!