I had never truly understood the versatility of matzo—the unleavened flatbread that is a symbolic and culinary focal point of the Jewish Passover feast—until I attended a seder with the family of my husband, Josh. I had eaten matzo every year at my family's seder table in memory of the Jews' flight from Egypt in biblical times, but in our barely observant house it was more a treat than a religious symbol. My dad liked to smear it with butter and make jokes about packing us ham and matzo sandwiches for lunch. In Josh's kosher household, by contrast, matzo was taken very seriously. His mother, Barbara, kept a few boxes of store-bought Manischewitz matzo in the cupboard during Passover, but there was also the harder-to-find shmura matzo. Remarkably thin and charred around the edges like a wood-fired pizza crust, shmura matzo is made exactly as prescribed by Jewish law: once the water is added, the matzo must be completely cooked in no more than 18 minutes, to preclude any rising.