Recipe by: Hershey's Combine cookie mix, egg, egg yolk, and vanilla in a small bowl. Cover; chill until firm, about 3 hours. Divide dough in half; roll each half to desired thickness on a lightly floured surface. Cut into desired shapes; brush with egg white. Place on a greased cookie sheet. Bake at 375 F for 8 to 10 minutes or until lightly browned. (Cookies spread considerably during baking.) Remove from cookie sheet. approximately 1-1/2 dozen cookies. Roll dough on a lightly floured surface to 1/4 inch thick. Cut into 2-1/2 inch circles. Place on a greased cookie sheet. Break a 1/2 pound Hershey's Milk Chocolate Bar into squares. Place a square in the center of each circle; place another circle on top. Seal edges with the tines of a fork. (Reserve remaining chocolate squares for the Pinwheel Cookies, below.) Bake at 375 F. for 10 to 12 minutes. Remove from cookie sheet. Cool on a wire rack. PINWHEELS: Makes approximately 3 dozen. Melt 4 ounces of a Hershey's Milk Chocolate Bar or remaining squares from the Surprise Cookies above; cool. Divide dough in half; roll out each half into a rectangle on a lightly floured surface to 1/4 inch thickness. Spread with melted chocolate; roll up dough from the long side. Wrap dough in plastic; refrigerate until well chilled. Cut into 1/4 inch slices. Place on a greased cookie sheet. Bake at 375 F. for 8 to 10 minutes. Remove from cookie sheet. Cool on a wire rack. ----