Combine the fish, curry paste, egg whites, fish sauce, and sugar in a food processor. Pulse a few times, to mix until it forms a smooth, thick, and sticky paste, 2 minutes or so. Once finished, poke the fish paste with a spoon. It should be firm, elastic, and springy. Transfer the fish paste into a big bowl.
Fold the green beans into the paste using a spatula.
Heat 1/2-inch oil in a small deep pot over medium heat until hot (*Footnote 4).
Work on the fish cakes in batches. Use a cookie scoop to transfer a ball of 2 tablespoons of fish paste onto an oiled spatula. Then use the back of another spatula or a large spoon to flatten the ball into a 1/4-inch (1/2-cm) thick disc. Gently slide the fish cake into the pan. Fry until the bottom side turns golden, about 30 to 40 seconds. Flip and cook the other side until golden. The whole process should take about 1 minute. (*Footnote 5) To test doneness, transfer a fish cake onto a plate and poke it with a toothpick. You should feel the bouncy resistance and the toothpick should come out clean.
Mix all the sauce ingredients in a small bowl right before serving.
Serve the hot fish cake with dipping sauce as an appetizer, or serve them on top of rice or noodles as a main. Enjoy!
You can store the cooked fish cakes in the fridge for a couple days, or in the freezer for up to 3 months. One note: do not refrigerate the uncooked fish paste. I did it once, and fried fish cakes made from day-old fish paste and it resulted in a tough and grainy texture. I had to put it back into the food processor and beat two more egg whites into it to get the texture fluffy again.
Catfish, sea bass, cod and other types of white fish fillets will work. Try to find the freshest fillets possible. I prefer to use catfish to make this recipe, because the fish is fattier and creates a better texture.
Authentic fish cakes use thinly sliced green beans or Chinese long beans (string beans) to add texture. You can skip this, or add a handful of chopped green onion.
To create the best fish cakes that have a crispy golden crust and tender interior, you need to use a bit more oil, just enough to cover the fish cakes. But if you do not like frying, you can add just enough oil to cover the bottom of the pan. The surface of the fish cakes will turn darker but it will remain tasty.
I highly recommend using a small, deep pot if you plan to fry the fish cakes. You can cook the whole batch with about 1 cup of oil (or less). The fish cakes cook very quickly in the hot oil, so you won’t be able to work on more than three cakes at a time. Alternatively, you can use a large nonstick skillet and roast the fish cakes with less oil.
If your fish cake turns dark brown too fast, not leaving you enough time to work on shaping the next fish cake, reduce the heat to medium or medium low. If the fish cake takes too long to turn golden, increase heat slightly.