Curry sauce is the basis for many Indian and Thai dishes, and these sauces are often very thick and creamy. Most of the time, the ingredients in curry sauces thicken the sauce properly without the need for additional thickening agents. Sometimes the vegetables and other ingredients in the curry add too much moisture to the sauce, making it runny. There are many different ways to thicken a curry sauce that has become too thin. It's important to choose a method that will not negatively affect the flavor of the dish; this can be achieved by either selecting a flavor-neutral addition or adding more of an ingredient that's already present in the dish.
Make sure the curry is allowed to simmer for the recommended amount of time before tampering with the sauce. Curry sauces take time to set up and often can appear runny or watery until the very last minute. Let the curry cook for the full amount of time listed in the recipe, stirring constantly to make sure it doesn't burn.
Scoop some of the curry sauce and vegetables into a food processor and blend it until smooth. Add the blended curry back to the main pot, stirring to combine. This is the best way to thicken a sauce without affecting the flavor of the curry, but it won't work for extremely thin sauces.
Add a spoonful of yogurt or 1/4 to 1/2 cup of coconut milk to the curry sauce and let it simmer, stirring constantly, for a few minutes. As many curries already contain one of these ingredients, this addition won't affect the flavor in many recipes.
Put a handful of raw, unsalted cashews or raw almonds in the food processor and pulse until they're a paste. Stir the paste into the curry sauce. If you don't have any cashews or almonds on hand, adding a spoonful of unsweetened, smooth peanut butter to the sauce works as well. This method will leave a distinct nuttiness in the sauce.
Put equal amounts of oil and flour in a skillet and, stirring continuously, cook the mixture over very low heat until it's lightly browned. Add about a cup of the thin curry sauce to the flour mixture and whisk until combined. Stir the mixture into the rest of the curry.