Put some water in a pot and bring to a boil. Add a pinch of salt and the nanohana, and cook until slightly softened, about 1 minute.Drain and rinse under cold running water, then squeeze out the excess liquid and chop, discarding the stems.
Put (A) in a saucepan and bring to the boil. Turn off the heat and add the nanohana, setting aside for 30 minutes.**If you’re in a big hurry you can proceed to step 2 without leaving to soak, but the bitter leaves and the savoury broth won’t have time to deepen and exchange flavours.
Drain the nanohana, reserving the liquid. Add the karashi paste to the liquid and mix well.
Serve the nanohana with the karashi dressing and add some katsuobushi flakes to taste.