The Portuguese tart has an interesting history. Back in the 1700s, it was common practice for monks and nuns to starch their clothing with egg whites. Rather than waste the yolks, they turned them into various cakes and pastries. Jerónimos Monastery in Lisbon got inventive and turned their yolks into pastéis de nata ("cream cakes").
When Jerónimos fell onto hard times, it and its popular recipe were sold to the local sugar refinery. The refinery opened a cafe, Pastéis de Belém, just to flog the tarts. It's still there today, owned by the same family. There are daily queues.
Of course, none of this will seem relevant or interesting when a few of the flaky, eggy, cinnamon- and icing sugar-sprinkled tarts get within your reaching distance. Head to Sydney's own Little Portugal (Petersham) to find the highest concentration – Gloria's and Sweet Belem are right across the road from each other.