Put butter into granite saucepan; when melted, add sugar and milk. Heat to boiling-point; then add chocolate, and stir constantly until chocolate is melted. Boil thirteen minutes, remove from fire, add vanilla, and beat until creamy and mixture begins to sugar slightly around edge of saucepan. Pour at once into a buttered pan, cool slightly, and mark in squares. Omit vanilla, if desired, and add, while cooking, one-fourth teaspoon cinnamon.