In a large bowl, cream butter and confectioners' sugar until light and fluffy, 5-7 minutes. In another bowl, mix flour, rosemary and salt; gradually beat into creamed mixture. Divide dough in half. Shape each into a disk. Wrap and refrigerate until firm enough to roll, about 30 minutes., Preheat oven to 350°. On a lightly floured surface, roll each disk to 1/4-in. thickness. Cut with a floured 2-in. round cookie cutter. Using a floured 7/8-in. round cookie cutter, cut out the centers of half of the cookies. Place solid and window cookies 1 in. apart on ungreased baking sheets., Bake until set, 9-11 minutes. Remove from pans to wire racks to cool completely., To serve, spread lemon curd on bottoms of solid cookies; top with window cookies. If desired, top with additional rosemary and confectioners' sugar.