Wash the chicken, set aside. Cut the leek in half and wash thoroughly. Cut it into 1-inch pieces.
When using Instant Pot, set it to "saute" setting and press "Adjust" once so it's switched from "Normal" to "More" for browning.
Saute the garlic, ginger, onion and leeks once it's hot. Stir occasionally until the they are softened.
Add the chicken, soaked shiitake mushrooms, bonito flakes, and water. Cover and use the "Manual" setting and set the timer for 90 minutes, and then do a natural release.
After the broth is done, turn off the instant pot and submerge the kombu into the broth for about 10 minutes to extract the flavor from Kombu. Covered with the lid.
After that, strain the broth using a colander (you can freeze the chicken if you wish and use it for other dish since we only need the broth).
Transfer the chicken stock to a large saucepan and bring it to a boil. in a bowl, add 1 cup of chicken broth and mix the white miso & red miso together, place the mixture in the chicken broth. You can now add the sesame paste or grind sesame (this is optional). Mix well. Add salt to taste.
Arrange your ramen noodles in a bowl, add the miso broth, and place any toppings that you like. I added the Chasu and the Ramen egg.