Eaten at Sofreh before, the four-year-old Persian restaurant in a Brooklyn brownstone, chances are you know its mast-o musir, a yogurt dip. The first things you see are chips of dried musir, the Iranian wild shallot, prized for its courtly but distinct whiff of garlic. Underneath this is a bed of musir-enriched yogurt. It has a richness that puts you in mind of custard and a sour streak that makes your mouth water. One of the original chefs at Sofreh, Ali Saboor, recently opened his own Persian restaurant in Brooklyn. Its name is Eyval, its neighborhood is Bushwick and its yogurt is even more delicious. Eyval has its own spin on mast-o musir, topped with some pickled musir in a spicy pool of turmeric oil. But the restaurant’s greater contribution toward advancing the cause of yogurt in New York City lies in Mr. Saboor’s reconsideration of another yogurt dip, or class of dips, called the borani.