Place potato in a medium saucepan; add water to cover. Bring to a boil, and cook 15 minutes or until very tender; drain in a colander, and set aside. Combine milk and green onions in pan, and cook over medium heat until thoroughly heated (do not boil). Add potato, salt, and pepper to milk mixture; beat at medium speed of a mixer until smooth.
Divide mixture evenly between 2 (8-ounce) ramekins coated with cooking spray; broil 5 minutes or until lightly browned.