Add the dried shiitake mushrooms and dried lily flowers to a bowl and cover with very hot water. Steep for 1 hour, or until softened and rehydrated.
Add the chicken stock, rice vinegar, soy sauce and hot sesame oil to a large pot. Bring to a boil over high heat.
Add the Sichuan peppercorns, mushrooms, lily buds, bamboo shoots, crushed red pepper, salt and pepper and stir. Reduce heat and simmer for 10 minutes.
Stir in the corn starch slurry and cook, stirring, 5 minutes to thicken.
Add the ground pork, and tofu. Stir and cook 5 minutes to cook the pork through.
Slowly drizzle in the beaten eggs while very slowly swirling the soup, 2-3 minutes. This will allow the eggs to form silky ribbons in the swirling soup. Remove from heat. Adjust to taste with vinegar for extra sour.
Serve the hot and sour soup into bowls and top with hot sesame oil or hot chili oil, scallions, and red pepper flakes.
