Summer Melon and Rose Water Dessert Soup

On December 22, the pre-Islamic Zoroastrian Yalda festival, modern Iranians celebrate the turning of the solar year by holding an all-night vigil, chattering and munching on good things in order to chase away evil. The most important good thing is an out-of-season watermelon, thought to be not only auspicious but good for the health in winter. Mehdi Shirvani, whose company, Mashti Malone’s, makes Persian ice cream in Los Angeles, tells me that his mother had a special room for storing melon