I don't think I would be wrong if I said that the best apple pie in town is served here, at Winkel. You just have to drop by one of the days when the Noordermarkt is open (Monday or Saturday) and you will see that due to the great demand of apple pie those days, they reduce the normal lunch menu.
Winkel is also a nice and inexpensive place for a beer, lunch or dinner (different menu every day). Website here.
Winkel is located in Noordermarkt 43