Simmer the pork leg bone to make a broth. In a separate pot, cook the fermented fish paste with water until boiling, stirring to dissolve, then strain to get a clear broth. Clean all the vegetables. Boil the snakehead fish, cuttlefish, and shrimp until cooked. Cut the roast pork into bite-sized pieces.

In a pot, sauté lemongrass stalks and minced lemongrass until lightly golden, then add minced garlic and chili and sauté until fragrant. Add the pork bone broth and strained fish broth, bring to a boil. Season with fish sauce, bouillon powder, and sugar to taste, then add chopped eggplant and cook until tender.