Wash and peel the yams and then slice and boil them in water for about 10 minutes.
*Tip: don't cover the pan, so you don't spread everything!
**Tip 2: no salt needed. The miso is already quite salty.
When they are very soft, mash the pieces with a fork, roughly.
Let it boil for 5 more minutes.
Add the miso spoon to the soup while it is still hot and stir well.
When the color is golden, add the green smell and serve immediately.