Although rich milk is traditional for mango lassi, butter-milk or yogurt may be substituted with equally delicious results. If mangoes aren’t in season, use mango pulp, available in Indian and Latin markets. For the best results, place both mango and milk in the freezer for 20 minutes before starting this recipe. And for a completely nontraditional but absolutely delicious rendition, try the Tropical Fruit Lassi variation.