In bowl, stir confectioners' sugar with milk until smooth; set icing aside. Preheat oven to 400 degrees . Line baking sheet with foil; spray with cooking spray. Unroll refrigerated piecrust on work surface; smooth with rolling pin. Trim each into 8-by-9-inch rectangle. Cut each again into 2-by-3-inch rectangle; transfer half to prepared baking sheet. Brush dough edges with egg. Spoon 1 tsp. fruit preserves (or chocolate-hazelnut spread) onto each rectangle. Cover with remaining rectangles; use fork tines to tightly seal edges. Poke holes in top of each pastry. Bake 12 to 15 minutes; cool on wire rack. Drizzle with icing.