Individually rinse the fish, squid and prawns in cold water and pat dry them separately with paper towel. Cut the fish and squid into a few chunks. (No need to cut the prawns) Put all of them into a food processor. Pat dry the onion with paper towel and put it into the food processor. Grind them finely. (It takes between 30 sec to 1 min). Move the ground mixture into a large mixing bowl.
Add the rest of the ingredients (egg white, rice wine, sugar, salt, starch and flour) into the bowl and mix them well.
Prepare one or two large flat plates and lay down some waxed paper (e.g. baking paper) on top. Shape the fish cakes the way you want and place it on the plate. Below is a short instruction on how to make fish cake balls and also fish cake long thin bars.-For balls: Scoop out 1 Tbsp of the fish cake mixture and take it out using another spoon (tea spoon size is good). Place the fish cake ball on to the waxed paper. Repeat this for the rest of the mixture. -For long thin bars: Cover the cutting board with a sheet of waxed paper. Scoop out some fish cake mixture (about 1/4 cup size) and flatten the fish cake with a kitchen knife. Roll it up with a knife (from left to right). Use both sides of the blade when you roll it – refer below photo. If you rolled it too thick, you can cut it into half. Repeat this for the rest of the mixture.
Put the water into a sauce pan and boil it for 5 mins on high heat. Once the water starts to boil add some fish cakes (about 5 fish cakes at a time) using tongs. Cook them until well done (when fish cake becomes firm – takes about 2 to 3 mins). Take them out with a strainer and put it aside to cool down.
Use this fish cake to make some Korean fish cake soup!