Persian Eggplant Dip with Walnuts

I first sampled this tangy dip at a Persian (Iranian) restaurant in New York called Persepolis. If you think baba ghanoush is good (see the next recipe), wait until you taste this. What makes this dip so distinctive is the addition of walnuts and a tangy farmer cheese called kashk-bibi. Before you despair of finding the latter (it’s available in Middle Eastern markets), know that its sharp flavor is easily approximated by using feta cheese and a spoonful of feta brine (the liquid in