Cut tofu into quarters. Slice cabbage into bite-sized pieces. Cut green onion diagonally into 1cm slices. Trim the root of shimeji mushrooms and separate them by hand.

Place oysters in a bowl with potato starch and gently rub. Add enough water to cover oysters and gently rinse. Repeat the rinsing process three times, replacing the water each time, then drain.

In a pot, add the seasoning ingredients (water, sake, dashi powder, ginger) and heat over medium heat. Once boiling, dissolve miso and add tofu, cabbage, green onion, and shimeji mushrooms. Cover and simmer on low heat for 5–6 minutes.