Put the onions garlic and green chilies into an electric blender. Add 4 to 5 tablespoons of water and blend until you have a smooth paste. Set aside. Combine the curry powder, anchoor masala, and cumin in a small bowl. Add 4 tablespoons of water, mix, and set aside. Heat the oil in a large, nonstick frying pan over high heat. When hot, put in the paste from the blender. Stir and fry for 8 minutes, or until it has browned a bit. Turn the heat to medium and put in the curry powder paste. Stir for 1 minute and put in the mango pieces. Stir once or twice to mix. Now put in 1 1/2 cups of hot water, the sugar, and salt and bring to a simmer. Stir now and then and simmer gently, uncovered, for 15 minutes.
Recipe courtesy of Madhur Jafferey, "World Vegetarian"