Cream butter; gradually add sugar, beating well at medium speed of an electric mixer. Add flour, egg whites, and vanilla; mix well. Divide a well-greased cookie sheet into four sections. Spoon 1-1/2 teaspoons batter in center of each section. Spread each portion of batter evenly with a spatula to make a 4x 3-inch oval. Bake at 425 degrees for 3 minutes or until edges are golden. Loosen cookies with a metal spatula, but leave on cookie sheet. Place one cookie upside down on counter, and quickly roll it lengthwise around the handle of a wooden spoon. Remove cookie, and let cool on wire rack. Repeat procedure with remaining cookies as quickly as possible. (If cookies become too stiff before rolling, return cookie sheet to oven briefly to soften them.) Continue procedure with ----