Apple strudel consists of an oblong strudel pastry jacket with an apple filling inside. Apple strudel dough is a thin, elastic dough. The oldest known strudel recipe is from 1696, a handwritten recipe housed at the Wienbibliothek im Rathaus. Whether as a type of sweet or savoury layered pastry with a filling inside, the strudel gained popularity in the 18th century.