As I get older, I become more nostalgic for the foods of my past. My grown children are also nostalgic, and their pasts are shorter than mine. They still talk about piroshki they ate years ago in San Francisco Russian restaurants that used to be on Clement Street. Alas, these little Mom and Pop places are gone, but obviously not forgotten. The piroshki recipe that follows is worth the effort to prepare. There are many different fillings, some with meat, some with cabbage; my favorite is wit