Beat butter until creamy, then beat in sugar and egg yolk.
Gradually work in flour to form dough.
Chill. Roll dough out into long ropes about ½ inch in diameter.
Brush ropes with lightly beaten egg white, then cut into 2½ inch lengths.
Dip each in pearl sugar to coat.
Place on greased baking sheets and bake at 350℉ (180℃) F 15 to 20 minutes.