Vico Geronimo alle Monarche 5.
This is in a lively square and many locals feel this is the only place to buy their pastries. There is always debate on whether Pintauro or Scaturchio is better. I think they are both equally good, although I like walking through the weaving streets of Spaccanapoli to Scaturchio and people watch in the piazza San Domenico Maggiore. There is more selection here. Try the sfogliatelle, millefloglie (similar to Napolean, layers of pastry with cream in between) and the cakes are also good.