Mince onion. In a large frying pan, heat oil on medium high heat and sauté onion until translucent. Transfer to a plate/bowl and let it cool.
Meanwhile put prawns in a large bowl and sprinkle corn starch. Rub them with hand and rinse in cold water. This is the best way to clean the shrimp/prawns. Drain well and set aside in a sieve.
Grind ginger and keep the juice as well.
Cut a prawn into 3-4 pieces and then pound it with a meat pounder or knife.
Chop green onions and whisk the egg whites until fluffy.
Combine shrimp, onion, green onion, ginger, ginger juice and salt, and pepper and mix well. Then add half of egg whites and corn starch. If the mixture is too runny, do not add any more egg whites. Otherwise use it all and adjust the consistency by adding more corn starch. Lastly add egg yolk and mix all together. The consistency should be fluffy but you need to be able to form a ball (but don't make it too hard).
Oil the plate with sesame oil and make about 1 Tbsp size ball shape.
Dredge in Panko. Instead of hands, it’s easier to use two forks or spoons, so it doesn’t stick to your hands. Try not to fold Panko inside the ball, and just apply it around the ball.
Deep-fry the shrimp balls about 4-5 pieces at a time so the oil temperature won’t drop too quickly. If you are new to deep-frying, here's my tip on deep-frying. When golden brown, take them out to a paper towel to drain extra oil. Serve with ketchup and salt & white ground pepper.
You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days or in the freezer for a month.