Grind ginger, garlic, cumin seeds, whole dry red chillies, cloves, cinnamon and mustard seeds along with malt vinegar into a fine paste. Heat oil in a kadai, sauté onions till soft and light brown.
Add tomatoes and cook on high heat till it forms a thick pulp and oil separates from the masala. Add the ground spices and stir-fry for two to three minutes. Add the shrimps and sugar.
Check seasoning and cook on low heat for another five to seven minutes or till oil separates from the masala. Make small holes in each puri and stuff it with the prepared Prawn Balchao.