Mix together the water and corn flour in a saucepan.. Reduce the flame and stir the mixture with a spoon until it thickens.
Gradually add the ghee. When the mixture thickens add the citric acid, kewra essence and red color. Gently mix and add half cup dried melon seeds.
Grease the tray with ghee and spread the mixture on it. Sprinkled with the remaining dried melon seeds and place in the fridge for cooling. Karachi halwa is ready.