What are "Euro" mirrors?
They should have been standard equipment on the TTR.
Go here to see a technical description of how they work.
Ignore the 'Boxster' content.
He does have some good install instructions that will work for the TT also.
Actually, the technical term is "Aspheric"
The Boxster Aspheric Mirror Page
These are the Audi Part Numbers;
Any dealer can order these.
8N0 857 535 A left
8N0 857 536 A right
Here is a picture form the back side.
Here is a picture of them installed on my car.