Soak the dried black mushrooms in warm water for about 5 hours until they are soft and pliable. Save 2 tablespoons of the soaking water. Rinse the mushroom well and cut into slices.
Rinse the fresh mushrooms well and cut into thick slices.
Dissolve the cornflour into the soaking water.
Heat a wok on the high heat. Add the oil and heat to 170 degrees C. Add the soaked mushrooms and the fresh mushrooms, and saute for about 5 minutes. Add the soy sauce, salt and sugar, and stir well. Add the wet cornflour slurry and toss thoroughly to coat.
Drizzle the sesame oil and transfer to a serving dish.