1. In a large pot, combine stock, ginger, lemongrass, dried shiitake mushrooms, mirin, kombu (if using), soy sauce, and peppercorns. Bring to a boil and then reduce heat and simmer on very low for 20 minutes.
2. Discard ginger, lemongrass, mushrooms, kombu, and peppercorns with a slotted spoon.
3. Add fennel and simmer for 10 minutes. Remove with a slotted spoon and set aside.
4. To cook fish, pat skin dry and sprinkle with salt. Heat oil in a skillet until very hot. Place fish into skillet, skin side down, and press down with a spatula for three to five minutes to achieve an even crisp. Flip and sear for another two minutes or until cooked through.
5. To serve: Place fennel in bowls with chopped kale. Top with fish, then add broth. Finish with radish, cilantro, sesame seeds, scallions, and lime wedge.
This broth goes really well with any white fish, or sous vide salmon. The fish can also be poached in the broth, if preferred.