Preheat oil for deep-frying. Prepare the batter only when you are ready to fry. Place beaten egg, self-rising flour, corn starch in a mixing bowl and add in the cold water. Using a chopstick or whisk to mix everything. You'll have some lumps in the batter and it's perfectly fine
Working in batches, dip each oyster into the batter until golden brown, about 2 minutes or so. Place on absorbent paper towel. Repeat until you are done with the oyster. Serve with some chili sauce