Final answer:
The correct answer to the starch-based breakfast item described by the legend is 'croissants,' which are flaky, crescent-shaped pastries associated with French breakfasts.
Step-by-step explanation:
The starch-based breakfast item that has been defined in the question is croissants. The legend mentioned in the question describes the origins of this flaky, crescent-shaped pastry. The story tells of bakers in Vienna who, while preparing their goods early in the morning, heard Ottomans tunneling to infiltrate the city and sounded the alarm. This act of vigilance is celebrated in the form of the croissant, which is popularly enjoyed as a breakfast item, especially in France.