Heat oven to 375 f. Coat baking sheets with non-stick cooking spray. In medium bowl, with wire whisk, combine cake flour, baking soda, and salt; set aside. In a large bowl, with electric mixer on medium speed, beat together prune puree, butter, sugar, brown sugar, egg, egg whites and vanilla 2 minutes or until creamy and light. With mixer on low speed, beat in dry ingredients just until incorporated. By hand, stir in chocolate chips. Drop by rounded tablespoonsful onto baking sheets; flatten slightly with back of spoon. Bake 10 to 12 minutes, until lightly browned around the edges. Let cookies cool on pan on wire rack 10 minutes before transferring to wire racks to cool completely. PRUNE PUREE: To make 1 cup, combine 1 1/3 cup pitted prunes and 6 tbs. of water in container of food processor. Pulse on and off until prunes are very finely chopped. Measure out 3/4 c. puree and set aside (the remaining 1/4 c. puree can be used as a spread in place of butter or fruit preserves.)