Pressure cook the potatoes till soft. Peel and mash. Set aside. Blend together the green chillies, garlic and ginger to a fine paste. Mix together the potato, onions, ginger/garlic/ chilli paste, coriander leaves, sugar, lime juice and salt to taste. Heat a little oil and add the mustard seeds and curry leaves. When the mustard crackles, remove from heat and add to the potato mixture. Mix well. Make a smooth batter with the bengal gram flour, salt to taste, cumin seeds,red chilli powder and turmeric powder. Add a teaspoon of hot oil when making the batter. Let the batter remain thick. Divide the potato mixture into equal sized portions, the size of a lemon. Dip each ball in the batter and deep fry till golden brown in color. Serve hot with chutney/ketchup.