Beat butter until creamy, then beat in sugar and egg yolk. Add vanilla. Gradually work in flour to form dough. Chill. Roll dough out into long ropes about 1/2 inch in diameter. Brush ropes with lightly beaten egg white, then cut into 2 1/2-inch lengths. Dip each in pearl sugar to coat. Place on greased baking sheets and bake at 350F 15 to 20 minutes. (C) 1992 The Los Angeles Times