Preheat oven to 325°F; grease two cookies sheets. Combine flour, cornstarch, and powdered sugar. Using pastry blender, cut in butter until mixture resembles coarse crumbs. Combine egg yolks and 1 teaspoon vanilla extract; add to flour mixture, stirring with fork until moistened. Knead dough in bowl to form a ball
In medium bowl, combine egg whites and remaining ½ teaspoon vanilla extract. In another bowl, combine remaining 3 tablespoons all-purpose flour and coconut flakes; add to egg white mixture; mix well
Shape cookie dough into 2/3-inch balls; roll in coconut mixture. Place balls 1-inch apart on prepared cookie sheets. Press a chocolate chip into each cookie’s center. Bake for 18-20 minutes or until cookies are lightly browned. Transfer to wire racks and cool completely.