Indians curries always begin with onions. When mixed together with another common curry ingredient, yogurt, this can provide all the thickening needed to create the spoon-rounding characteristics of an outstanding Indian curry. Characteristically made by the continual adding and toasting of dry ingredients, followed by the introduction of liquid, the onions and yogurt together form the base of the flavor of many Indian curries and work to thicken a curry by time it is done simmering.

Potatoes are a common ingredient in many Indian curries and serve a dual purpose with their inclusion. They both bulk up the dish and help to thicken it. Smash well-softened boiled potatoes with a spoon or fork on the inside of the pot as you stir the curry to incorporate the potatoes into an overly liquid curry. The main thickening agent for egg curries of Northern India, potatoes are present in many wide-ranging India curries to help add some thickness to the finished product.

Lentils are another popular means of bulking up and thickening an Indian curry. Widely used in both meat and vegetarian curries, many far-reaching different types of curries call for a small amount of lentils to be added for this reason. While solid for much of the cooking, after prolonged simmering, the lentils swell and easily lose their shape in the curry as they thicken it. Add just a tablespoon or two to a watery curry and cook them until they become tender to thicken your curry.

South Indian curries rely heavily on coconut products to thicken curries. Grated coconut, coconut cream and coconut milk are all effective thickening agents for different types of curries. Imparting a slightly sweet flavor on the curry, coconut products work best in masala-style curries, or ones that are made using ground spices and coconut to make a sweet, brown comforting sauce. Coconut milk and its flesh burns easily and for this reason is always added at the end of cooking to create a thick sauce.