If you are about to visit Vienna, you have to stop by at Schillinger in Großmugl! It is 100% vegan and you can eat traditional austrian cuisine (like Wiener Schnitzel, Backhendl, etc.) there. They have fantastic deserts (try Tiramisu Nockerl), ice cream and several cakes.
You can reach Großmugl by car (about 30 minutes) or by bus (Bus 436 from Stockerau to Großmugl Hauptstraße).