Anton
Google
This is as good as it gets!
According to my local friends, Manteigaria is the "second best" in Lisbon. So if you don't want excessive queues, or to go out of your way, then just drop by here. They have a bunch of outlets around the city.
After having tried a couple different places including Rossio for pastel de nata, I can say this one is legit 👌🏼