Melt the butter in a pot, then stir fry the Shiitake and thinly sliced onion until tender.
Add A to 2., cover with a lid, and bring to a boil, then simmer on low heat until the rice is cooked through.
Blend 3. in a food processor until smooth and let it cool. Sprinkle with pepper and fresh cream, to taste.
Rehydrating dried Shiitake with cold water gets rid of bad odors and brings out more sweetness and flavor. https://shiitakejapan.com/en/how-to-rehydrate-dried-shiitake-for-maximum-flavor.html
(←the most delicious way to rehydrate Shiitake)
Thinner KOSHIN Shiitake are easier to rehydrate)