If using dried shiitake and wood ear mushrooms, rehydrate them by submerging them in hot water for 15-20 minutes till they soften up. Reserve the water to be used as stock in the soup. Slice all the mushrooms and set aside.

Heat oil in a pan and add red chillies and ginger. Saute till the ginger is golden brown and add the garlic. Saute the garlic for a few seconds and add the celery and carrots.

Cook the carrots for a minute or two and add mushrooms, tofu, chicken, both the soy sauces and six cups water to the pot (if using the stock from mushrooms, reduce the water to 5 cups and add the stock). Bring the pot to a boil and simmer for 5-6 minutes.

Stir together cornstarch in 1/4 cup water and slowly add it to the pot while stirring continuously. Bring the soup to a quick boil. The soup should start to thicken.

Slowly add in the beaten egg, swirling with a ladle as you go to create egg ribbons in the soup. Stir in rice vinegar, white pepper, salt (if using) and sesame oil. Turn off the flame. If the soup is too thick for your liking, add a little water or stock to thin it. Serve hot.