Simmered japanese butterbur (fuki no nimono)

1 bunch Japanese butterbur
1 2/3 cups (400 ml) soup stock
sake, mirin, salt, soy sauce

1. Prepare big pot, and cut Japanese butterbur into shorter than diameter of pot.
2. Rub Japanese butterbur with salt on the cutting board.
3. Boil enough water (a copper pot is more better, because Japanese butterbur become bright green).
4. Put Japanese butterbur in thickness order and boil 2-3 minutes.
5. Soak boiled Japanese butterbur in cold water, and string.
6. Cut Thick part lenghtwise into four, and cut it into 2 inch pieces.
7. Boil 1 2/3 cups (400 ml) soup stock, add Japanese butterbur, 2 tablespoons sake, 1 tablespoon mirin and a pinch of salt and soy sauce.
8. Boil again, take harshness carefully.
9. Stop to heat, leave overnight.