Clean and devein 500 grams of prawns, leaving the tails intact. Pat them dry and set aside.
In a mixing bowl, add 100 grams of gram flour (besan), 2 tablespoons of rice flour, 1 teaspoon of red chili powder, 1/2 teaspoon of turmeric powder, 1 teaspoon of ginger-garlic paste, 1/2 teaspoon of garam masala, 1/2 teaspoon of carom seeds (ajwain), and salt to taste. Mix well.
Gradually add water to the dry mixture and whisk until you get a thick, smooth batter.
Add the cleaned prawns to the batter and mix well, ensuring that each prawn is well coated with the batter.
Heat oil in a deep frying pan or kadai over medium heat. Once the oil is hot, carefully drop the batter-coated prawns one by one into the oil.
Fry the prawns for 3-4 minutes on each side, or until they turn golden and crispy. Ensure not to overcrowd the pan.
Use a slotted spoon to remove the fried prawns from the oil and place them on a paper towel to absorb excess oil.
Serve the Prawn Koliwada hot with mint chutney or ketchup.