Sauté onion in butter in a large Dutch oven until tender; add flour, stirring until smooth. Cook, stirring constantly, 4 minutes or until mixture is browned. Stir in spinach; simmer 10 minutes or until tender.
Place spinach mixture and 1 cup chicken broth in container of an electric blender; process until smooth. Return spinach mixture to Dutch oven. Stir in remaining chicken broth, whipping cream, salt, nutmeg, and pepper. Heat thoroughly. (Do not boil. ) Serve warm in individual soup bowls; sprinkle with paprika, if desired.