Remove the legs and wings from the chicken and set aside. Cut the meat off the breast bone, reserving the carcass. Remove the skin from the breasts and legs and spread the skin, fat-side down, on paper towels or paper plates to dry. Reserve for Gimme Some Skin (see separate recipe).
Halve a large onion, leaving the skin on, and place it cut side down in a 6- to 6 1/2-quart stovetop pressure cooker. Sear it over high heat, 4 to 5 minutes. Remove the pot from the heat.
Add the 2 halved carrots, 2 halved celery stalks, leek tops and dried mushrooms to the pot. Then add the chicken carcass, legs, thighs and wings with the peppercorns and bay leaves. Add the water and use tongs or a wooden spoon to push as much of the chicken under water as possible.
Attach the pressure cooker's lid and heat on high. When full pressure is reached, about 5 to 10 minutes, lower the heat to medium-low. (You shouldn't hear the whistle, only a soft hiss). Cook 30 minutes.
Remove the pressure cooker from the heat and release the pressure by placing the cooker in the sink and dousing with cold water for one minute. Then release the pressure lock and remove lid.
Strain the solids first through a colander, then a fine sieve or cheesecloth.
Return the stock back to the pot. Add the shoyu, togarashi, lemon juice and chicken breasts to the pot and bring to a boil (without the lid), then reduce the heat to low. Simmer 5 minutes.
After 5 minutes, check the breasts for doneness (I usually pull them at 150 degrees F) and remove to a large bowl. Add the remaining diced carrots and parsnips to the broth and simmer 3 minutes more. Then add the remaining diced celery and leeks. Kill the heat and allow to sit for 3 minutes, then taste the broth and correct with salt and/or lemon juice to taste.
Since they're so hot, shred the chicken breasts by either pulling apart with two large forks or hit them with a hand mixer on low…that'll do the trick, too.
To serve, ladle soup in the bowls, top with some of the breast meat, garnish with the celery leaves and serve with chicken skin "sandwiches." (See separate recipe for Gimme Some Skin.)
Like any soup…this one is better the next day. Oh, and discard the solids from the pressure cooker…they've given their all.
Togarashi mixtures vary greatly, so start with a teaspoon and add more as needed.