Cut the eringi mushrooms in half lengthwise, then cross-cut them. Remove the stems from the shiitake mushrooms and slice them into 1cm wide pieces.

Heat a frying pan over medium heat and add the butter. Once the butter is half melted, add the eringi and shiitake mushrooms and sauté for 3–4 minutes.

Drizzle soy sauce over the mushrooms and mix well.