It is called "Nähkontor" and it's located in Prenzlauer Berg. When I first came in there, I was pleased by the nice 1950s interior. They did a great job with that, its like you go shopping through a time machine. You can get everything the sewing heart desires (fabric, notions etc.), but they also offer sewing classes and services like self-fabric covered buttons and belts. I didn't know that this services is offered by here in Berlin.
If you like sewing (I guess so) and if you're in Berlin and maybe you have a faible for vintage interior and notions (I obviously have.), that's your place.