I specifically had mine at Casa Pastéis de Belém purely because they are the very first pastry shop opened since 1837 selling these tarts; who up till now still kept their ancient secret recipe! Mind you this bustling shop is ever so packed with people that you'll need to be quick to spot a table or join in the long queue for takeaways. Don't worry if you can't make it to this shop coz there are always other options since bakeries selling Portg' tarts are scattered everywhere.
...As for my preferences since ~ I'm in lurveee with puff pastry Portugese style than the short crust type.
Its worth! Its delicioso!