Khatta literally means sour and that is really what this dish is all about. Its a scrumptiously sour gravy which is made of amchur powder which is basically a spice made by pulverizing dried green mangos. The way I like making khatta is with fried besan ka boondis (fried chick pea flour balls) but this can be substituted with regular chickpeas too. You can make your own the boondi or buy it. A good brand of Boondi is Haldirams and is available at any Indian grocery store.