Steps

1. Measure out 200g all-purpose flour, 90g water, and 10g salt. Sift the all-purpose flour into a bowl lined with a damp cloth. (Key Tip!) The amount of salt and water may need adjustment depending on the season, temperature, and humidity, but this ratio is fine for home cooking.
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2. Add all 90g of water and 10g of salt to the sifted all-purpose flour in the bowl. Mix well until the salt dissolves. (Key Tip!) It's crucial to dissolve the salt thoroughly.
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3. Make a well in the center of the sifted all-purpose flour and add about 2/3 of the salt water.
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4. Once the salt water is added, quickly mix the dough with your fingertips, covering the water with the dough. Break up any lumps and combine with the surrounding flour. Gather the flour from the bottom of the bowl and mix with both hands in a prayer-like motion until it forms a coarse, crumbly mixture.
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5. Add the remaining salt water and mix by breaking up the clumps with your fingertips. Once the flour is no longer visible and it forms small granules, mix by rolling with your palms until it comes together into a ball. (Key Tip!) If you're experienced, you can leave a little water to adjust the consistency here.
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6. Place the gathered dough into a bag and let it rest for at least 1 hour (about 3 hours in winter). (Key Tip!) Resting the dough is essential for udon.
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7. While the dough is still in the bag after resting for about 1 hour, step on it with your feet. Once it has stretched to some extent, gather the dough into a ball within the bag and step on it again. Repeat this process about 3 times. (Key Tip!) Using a vacuum seal bag or a ziplock bag is recommended. If you have a large amount, sandwich it between bags and step on it.
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8. Return the stepped dough to the bowl, fold it towards the center to form a ball, and press the center firmly with your thumb to shape it.
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9. Turn the dough over, return it to the bag, and let it rest again for at least 1 hour in summer or 2 hours in winter. (Key Tip!) Resting the firm dough makes it easier to roll out.
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10. Dust the dough that has rested for about 2 hours with flour. While still in the bag, or by hand, press the dough outwards from the center to form a round shape. (Key Tip!) Cornstarch (mochi-tori-ko) is ideal, but potato starch can also be used as a substitute.
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11. Once the center is puffed up, press the center to evenly flatten it, creating a diameter of approximately 20cm.
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12. Roll out the dough with a rolling pin. First, press from the center upwards, rolling in a wave-like motion to maintain a round shape, and spread it to a thickness of no more than 5mm, to about 26cm in diameter. (Key Tip!) Work with the feeling of pressing rather than rolling.
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13. Shape the floured dough into a square. Roll it onto the rolling pin from the front, rotate a few times to stretch, and then change the direction of the rolling pin to 180, 90, and 45 degrees, while pressing to create corners and ensure even thickness.
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14. Use a 'cat's paw' motion to apply even pressure throughout, finishing with a dough that is approximately 39cm long, 37cm wide, and 2mm thick. (Key Tip!) The noodles will expand about 1.5 times when boiled, so it's best to make them relatively thin.
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15. Fold the floured dough in half.
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16. Place the dough on a cutting board generously dusted with flour. Trim off the very first fold and cut to your desired thickness. (Key Tip!) Use plenty of flour to prevent the noodles from sticking together.
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17. If using a noodle cutter, point to the center with a finger, lightly rest your hand on the guide board, and repeat cutting and lowering. Lift the cut noodles with the knife, allowing the flour to coat them, and tap off any excess flour.
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18. Carefully add the noodles, separated, to a large pot of approximately 5.5 liters of boiling water. (Key Tip!) Using the largest pot possible is recommended.
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19. Stir gently to prevent the noodles from sticking. Reduce the heat only when it's about to boil over. Do not add cold water, and boil for about 6 and a half minutes.
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20. The noodles are done when they become translucent and the cross-section is no longer powdery. Drain the water, and depending on the season, shock them in ice water. (Key Tip!) If you're unsure about the cooking time, take out one noodle, cool it in cold water, and taste it.
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