1.Make the soup stock In a big cooking pot, add about 2L water and bring it to a boil. Once it boils add the chicken.
2. Bring it to a boil again, then remove from the heat. Cover and leave it for 1 to 2 hours.
3.Meanwhile make the soup base
In a heat-safe bowl, add katsuo flake, garlic and kosher salt and set it aside. In a small cooking pot, add leek, sesame oil and vegetable oil. Bring it to a boil and once it is boiling, simmer for 3 minutes.
4. Then immediately pour this oil mixture into a bowl. Mix well.
5. Add kobucha, chicken powder and boiled water. Mix well : the salt should melt completely. Set aside. You can leave it until the chicken is ready.
6. Using a cooking sieve, strain the soup base into another bowl. Press or squeeze well against the sieve.
7. Transfer the sieve residual into another bowl and blend it with your hand blender until it is smooth like a paste.
8. Remove the chicken from the water and cut it in slices. Set it aside. With the soup stock, strain once and add more water to reach a total of about 2.5L (it's about 500ml per person) then bring it to a boil.
9.Prepare the noodles Cook your ramen according to the package instructions. Place 2 to 3 tbsp (or more) soup base into your serving ramen bowl, add the boiled soup stock, then place the cooked ramen into the soup.
10. Top your ramen with chicken, leek, egg etc.....Sprinkle sesame, and enjoy :)