Heat the oil in a nonstick saucepan over moderate heat. Add curry paste and turmeric and stir often until mixture sizzles, about one minute. Add peanut butter, coconut milk, water, fish sauce, lemon juice, and sugar and reduce the heat to low. Stirring constantly with a whisk, cook for three minutes.

When mixure begins to bubble, remove from heat, and continue to stir.

If sauce is too thick, thin with water.

Taste and adjust seasonings to an interesting balance of sweet, salty, and spicy flavors.