Make the marinade by mixing together the sugar, salt, soy sauce and cornflour slurry. Mix in the chicken, let marinate for 15 minutes.
Meanwhile, blanch the tofu in boilling water for 2 minutes. Drain and place back into the saucepan.
Separate the egg yolks from the egg whites. Mash the egg yolks with 1 tablespoon water. Finely dice the egg whites. Set aside.
Heat a large frying pan with 1 tablespoon oil over high heat. Stir-fry the garlic until fragrant, 2-3 minutes. Add the aubergine and stir for 2-3 minutes. Add 2 tablespoon water and mix well, stir until dry. Repeat this procedure until the aubergine are soft and cooked through. Drain well and set aside.
Heat the same frying pan with 1 tablespoon oil over high heat. Stir-fry the chicken until cooked through, 3-5 minutes. Set aside.
Heat the same frying pan with 1/2 tablespoon oil over medium heat. Stir-fry the mashed egg yolk. Add the chicken, egg whites and fish sauce. Mix well and set aside.
Transfer the aubergine over the tofu in the saucepan, then top with chicken. Add the dark soy sauce, chicken stock and water, stir to mix well. Heat over high heat until the mixture boils. Stir in the cornflour slurry to thicken the sauce. Add the spring onions and serve.
Salted duck eggs can be purchased in Chinese/Oriental speciality stores.