1. In a large mixing bowl, sift corn flour, and plain flour.
2. Add baking powder and baking soda to it.
3. Throw salt and lightly beaten egg.
4. Add water and ice cubes in it. Stir to incorporate. Do not over mix.
5. In a frying pan, heat oil. Dip prawns in the batter, and drop it in hot oil.
6. Do not over crowd the pan. Cook until golden brown.
7. Sprinkle salt and pepper on top, and serve prawns hot with tomato sauce.