Soak the mushrooms in warm water for 30 minutes. Cut the carrots into small sticks. Slice the zucchini and bell pepper into thin strips. Trim the snow peas. Chop the onions and celery. Drain the mushrooms and cut them into strips. Blanch the soy sprouts in boiling water for 2 minutes. Drain. Melt the butter in a pan and add the vegetables in the following order, stirring constantly: onions, celery, snow peas, zucchini, carrots, bell peppers, mushrooms, and soy sprouts. Drizzle with soy sauce and sprinkle with white pepper. Cook for 15 minutes, the vegetables should be cooked but still crisp. Serve with rice.