Remove cartilage from crabmeat. Dissolve bouillon cube in water.
In 4-quart saucepan, cook onion in butter until tender. Blend in flour and seasonings. Add milk and bouillon gradually and cook over medium heat, stirring constantly, until mixture thickens enough to coat spoon. Add crabmeat; heat, do not boil. Garnish with parsley flakes before serving.
Note: Soup improves upon standing as flavors get a chance to blend, so this is a good “prepare ahead: dish. Let mixture come to room temperature and then refrigerate until ready to use. Reheat over very low heat, stirring often, until soup is hot, but not to the boiling point.