Heat oil in a deep-fryer to 190 degrees C (375 degrees F).
Whisk flour, corn flour, and salt in a large bowl. Make a depression in the center of the flour. Stir in the water and egg yolk. Mix just until moistened; batter will be lumpy. Stir in egg whites.
One at a time, dip prawns into the batter to coat. Do not batter tails. Carefully place a few prawns at a time into the hot oil. Fry until golden brown, about 1 1/2 minutes. Drain on paper towels.
We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. The exact amount will vary depending on cooking time and temperature, ingredient density, and the specific type of oil used.