Combine butter or margarine and flour in a small bowl; cream with the back of a spoon until smooth.
Stir in sherry and egg yolk.
Add crabmeat and white pepper; stir until blended.
Dust your hands with flour.
Shape rounded teaspoonfuls of dumpling mixture into small balls.
To cook, drop dumplings in simmering soup 15 minutes before soup is done.
Cover and simmer until dumplings are firm, about 15 minutes.