Preparation

• Put the bean curd in a zip-top freezer bag and freeze for 24 hours. Thaw at room temperature until soft enough to slice, about 1 hour, and then cut into 3×1/4-inch strips; set aside.
• Put the cloud ears and lily buds in separate bowls, cover each with hot water, and soak until soft, 20 to 30 minutes. Keeping them separate, drain the cloud ears and lily buds, rinse well with cool water, and drain again. Break the cloud ears into small pieces; set aside. Remove the hard stem ends from the buds, halve crosswise, and set aside.
• In another small bowl, whisk the cornstarch with 3 Tbs. water until smooth; set aside.
• Put the broth and 1 cup water in a 4-quart saucepan, cover, and bring to a boil. Uncover and stir in the ginger and preserved vegetable. Return to a boil and cook, uncovered, for 2 minutes. Stir in the lily buds and cloud ears, return to a boil, and cook for 1 minute. Stir in the bean curd, bamboo shoots, and hot pepper oil. Return to a boil and cook for 2 minutes. Add the pork and any juice from the bowl, return to a boil, and cook just until the pork turns white, 1 to 2 minutes. Stir in the vinegar.
• Stir the cornstarch mixture to loosen it and then, using a ladle, stir the soup in one direction while you pour in the cornstarch mixture. Stir until the soup thickens and returns to a boil, about 2 minutes. Add the eggs in the same way. The soup will be thick and opaque. Stir in the soy sauce and sesame oil, and remove from the heat. Season to taste with more hot pepper oil or vinegar to achieve a hot and sour balance that you like. Serve garnished with the scallions.