It exists because Napoleon's occupying troops wanted croissants, and Hamburg's bakers, working with heavier northern dough, could only half-deliver — the flattened, cinnamon-swirled result stuck.
A laminated, buttery dough is rolled with cinnamon sugar, then pressed flat into a squashed spiral before baking, giving it crisp caramelized edges and a soft center. It's a breakfast and coffee-break fixture sold from bakery counters and train-station kiosks all over the city.