Daulat ki chaat appears in the lanes of Chandni Chowk only in the coldest months, from about November to February. Vendors whisk milk and cream through the night and leave it out under the winter dew, then skim off a foam so light it disappears on your tongue, topped with saffron, khoya, sugar and pistachios. It's sold before the sun gets high, because warmth destroys it. A home kitchen can't recreate a Delhi winter night, so this version uses very cold milk and cream whipped to a loose foam and layered with saffron. It comes close: airy, cool, faintly sweet. Chef's tip: chill everything, bowl and whisk included, for at least 4 hours; the colder the milk, the more stable the foam.