Sweet and Sour Cod

 First remove the internal organs and fins from the snakehead fish. Scrape off the silver-white outer membrane on both sides, then rinse thoroughly with running water, and dry the surface of the fish with kitchen paper.
Cut off the head of the snakehead fish. Slice the fish body into 6 cm long segments. Coat the surface evenly with a layer of flour. Chop the large onion diagonally into sections. Slice the old ginger thinly. Pan-fry over high heat in a flat-bottomed pan until the oil is around five (when you place your hand above the pan, you can feel the steam).Lay out the segments of snakehead fish in the pan and fry for about 5 minutes on one side until it turns golden   yellow. Flip the pieces to fry the other side until equally golden yellow, then remove and drain off the excess oil.
Pour the remaining oil from frying the snakehead fish into a wok and heat over high heat until around five (when you place your hand above the pan, you can feel the steam). Add the chopped onion sections and ginger slices to stir-fry until fragrant, then add the fried snakehead fish segments.Season with soy sauce, white sugar, cooking wine, salt, andwhite pepper, stirring evenly.
Add about 400 ml of warm water to the pot, bring to a boil over high heat, then reduce to low heat and cover. Simmer for about 15 minutes.  When the liquid in the pot is mostly reduced, add vinegar, stir gently, then continue cooking with the lid on for about 3 more minutes before finishing. Sauté sugar, Shaoxing wine, salt, and white pepper powder evenly.Powdered white pepper flakes are added and sautéed evenly.
5 Add about 400ml of warm water to the pot, bring to a boil over high heat, then reduce to low heat, cover, and simmer for about 15 minutes.
6 When the moisture in the pot gradually dries up, add the malt vinegar and stir-fry slightly evenly.
7 Finally, cover and continue to simmer for another 3 minutes before finishing.