Here is a portuguese egg tart, this is what came up when I searched for "portugisisk æg": https://www.colourbox.dk/preview/7168057-portuguese-egg-tart.jpg
I know what a Portuguese egg tart is (and I love them very much) but that's, I assume, not what they are talking about. Maybe.
(They are portugisisk æg tærte, by the way.)
That would be too many consonants at once. Tha adjectives that end on -sk don't have a -t form.