What do the Austrians call (in German) that yogurt filling that they put in many of their delectable cakes?

Are you sure these were yogurt fillings? Typical tortes (Black Forest Gateau, for instance) come with a whipped cream cream filling; this is called Schlagobers in Austrian German and Schlagsahne in standards German. If it's on the rich side, the cake may be made with butter cream (Frankfurter Kranz, for instance).
Yogurt on its own is too runny for a cake filling and needs some gelatine or similar stuff to stay in place.
But there exist many cakes with Topfen/Quark/Ricotta/Séré filling, often mixed with cream (Rahmquark etc.)

Thank you, abalada! "Topfen" must be what they called it! I remembered "Topf" and looked it up online but didn't come up with what I expected.
I asked at the first cafe I was in on my recent visit there (Diglas), and the waiter told me it was yogurt.
And thanks to the rest of you for your input.
mike9, it's always coffee time!
Oh, how I miss that excellent coffee and fantastic cake! boohoo...
The waiter probably couldn't think of a better English word.
Topfen is sort of like cream cheese (which is generally known to Austrians by the biggest US brand name [i]Philadelphia[/i]), but is a little sour and not as rich as cream cheese.
It resembles crème fraiche, but is more 'solid'.
It's not just in cakes, either.....