In a mixing bowl, combine the white miso paste, soy sauce, sesame oil, rice vinegar, sugar, minced garlic, and grated ginger. Mix until smooth.

Set the marinade aside to let the flavors meld.

In a large bowl, add the sliced shiitake and button mushrooms.

Pour the miso marinade over the mushrooms and toss until they are evenly coated.

Let the mushrooms marinate for at least 10 minutes.

Heat a skillet over medium heat and add the marinated mushrooms along with the marinade.

Cook for about 5-7 minutes, stirring occasionally, until the mushrooms are tender and the marinade has thickened slightly.

Remove from heat and transfer the mushrooms to a serving dish.

Garnish with chopped scallions and toasted sesame seeds before serving.