This is an exotic sauce that is simple to make. Soursop is a tropical fruit found in Central and South America and the Caribbean. It has a naturally sweet and sour flavor profile and a milky white consistency when puréed. Called guanabana in Spanish, soursop is often used in fruit shakes and ice creams. You can find frozen puréed soursop in the freezer section of Caribbean and Spanish markets or, often, in the Latino foods section of traditional supermarkets. We like to use this sauce as a substitute for traditional Chinese sweet and sour sauces in chicken and vegetable stir-fry.