"Yellow curry" is a fairly generic culinary term for a powder, paste or sauce that has a yellow color, usually as the result of spices such as turmeric and chili powder. In Thai cuisine, however, yellow curry is a specific type of sauce that is made from a variety of ingredients, descended in part from Indian curries and Muslim cooking techniques. The curry has a mild level of spicy heat but a very complex and rich flavor derived from the layers of spices that are used. Although recipes vary, the common ingredients in most yellow curry include cumin, turmeric, coriander, lemongrass, onions, peppers, garlic, ginger and fish sauce. The spices can be cooked in different ways to develop their flavors, or they can be mixed together raw and cooked later when used in a larger recipe.
Several of the ingredients in a Thai yellow curry can have their flavors changed slightly through cooking. Cumin, coriander and turmeric can all be roasted in a pan for a deeper, smokier flavor. The onions, fish sauce, lemongrass and peppers can be fried for different amounts of time so any sharp, uncooked flavors are removed. One method is to roast or cook only half of the spices, leaving the other half uncooked so different layers of flavor develop, especially when the yellow curry is eventually cooked itself.
When the ingredients for yellow curry are mixed together, they are either ground in a mortar and pestle or blended in a food processor. In general, no significant amount of extra liquid is added to the curry when it is blended; it instead relies on the natural moisture in the ingredients to form a thick paste that can be thinned later while cooking with water or stock. Some recipes, however, do call for the addition of coconut milk or coconut cream after the paste is made to make the curry into a thick, rich sauce.
After yellow curry paste is made, it can be used to flavor a wide array of dishes. One of the most common is a yellow curry chicken, in which the chicken is fried with vegetables and the paste is added with some water or stock to form a thick sauce that coats all the ingredients. It also can be used to add flavor and spice to soups. In some preparations, the curry is first used as a marinade for meat or other ingredients and then is added to the pan to cook with them.