* Alternatively, you can buy mentsuyu, a pre-seasoned dashi stock.
1. First, make the dashi stock. Heat the konbu in a pot with 6 cups of water, and remove it just before the water comes to the boil. Add the bonito flakes, remove from the heat and set aside for 10 minutes before filtering through a fine sieve. Flavor to taste with soy sauce and mirin.
2. Boil the dried soba noodles in plenty of water for about 7 or 8 minutes (set aside the leftover cooking water). Drain the noodles in a colander and rinse well immediately.
3. Cut the chicken into small 3-4cm pieces, and cut the leek into diagonal slices. Bring the dashi stock to the boil, and add the chicken followed by the leek. (Cook for how long?)
4. Reheat the soba in the water that you set aside earlier, drain in a colander, and place in a bowl.