It's deep-fried yeast dough dressed like a pizza — garlic, sour cream, and grated cheese piled on top — a combination that sounds improvised because it basically was.
A yeasted potato dough is stretched thin and deep-fried until puffed and golden, then rubbed with garlic and topped with sour cream and shredded cheese. Vienna's Naschmarkt and street festivals sell it hot, folded into paper for eating on the move.