Liliana d’Ambrosio’s pizza rustica is amazingly versatile. Cut it in small squares and serve it as an appetizer or part of a buffet. Make it the centerpiece of a brunch, a light lunch, or Sunday night supper. Liliana always bakes it the day before she plans to serve it and leaves it at room temperature. I’ve even seen her make calzoncini with this pastry, shaping tiny little envelopes of dough that enclose the same filling, frying them until they are golden, and then servin