Take onion and tomato and grind them separately.make puree

After roasting masala add onion puree. Sauté till light brown. Add tomatoes puree and ginger chilli paste. Add salt, red chili powder, turmeric and coriander powder. Let it cook for 1 minute. Add boiled potatoes. Add 1/2 cup of water and cook for 1 - 2 minutes