To make dashi:
- In a bowl, soak the kombu in water for 15 minutes or overnight.
- In a small pot, bring the kombu and water to almost a boil. Remove the kombu right before boiling to prevent the dashi from developing bitterness and a slimy texture. Then add katsuobushi and simmer for 15 seconds. Turn off the heat and set aside to let it steep for 15 minutes.
To make Chicken Udon:
- Cut leeks into small rounds and chop green onions to small pieces.
- Cut the chicken into bite size pieces.
- Heat oil in a non-stick frying pan over medium heat. Add the chicken and brown the meat on both sides. If you have a large non-stick pot, you can just use the pot instead of non-stick frying pan.
- Add the leek and sauté for 1 minute to coat with the oil.
- Transfer the leek and chicken to the large pot. Then pour the dashi into the pot, straining through a sieve to capture katsuobushi. Discard the katsuobushi.
- Bring the soup mixture to a boil, skimming the scum and foam with a fine mesh sieve as it cooks.
- Once boiling, reduce heat to simmer and add the Seasonings.
- Cook the udon noodles according to the package instructions. If you use frozen udon noodles, it takes 1 minute to reheat. Drain well and transfer the noodle to the bowls.
- Add some chopped green onions into the soup pot right before serving.
- Serve the chicken and soup over the udon noodles in the bowl. Sprinkle more chopped green onion and shichimi togarashi, and enjoy immediately.
Chicken thighs: Use skin-on chicken thighs for a flavorful result. Usually they are bone-in, but you can ask the butcher to remove the bones.