How to remove sand from clams before cooking:
First, wash clams with tap water and drain. In a shallow container, spread clams and add 4 cups water and 3 Tbsp salt. Let it sit in a refrigerator for about 24 hours.
Wash rice, drain, and let sit for 10 minutes.
Mix Soup Stock ingredients.
In a pot, combine rice and soup stock. Add whole shiitake and eryngii mushrooms on top.
Bring to boil over high heat without lid, stirring occasionally.
Once boiled, reduce the heat to low and cook 10 more minutes with the lid on.
Add the clams and cook on low heat for about 1 minute. Turn off the heat and let it simmer for an additional 10 minutes, or until clams' shells open up.
Mix well and add mitsuba to taste.