Preheat your air fryer to 375°F.
Roll out the puff pastry sheet and cut it into 12 equal squares.
Place each square into a muffin tin, pressing the pastry down to form a cup shape.
In a medium-sized bowl, whisk together the sugar, flour, and salt.
In a separate bowl, whisk together the milk, egg yolks, and vanilla extract.
Pour the milk mixture into the sugar mixture and whisk until well combined.
Pour the mixture into each pastry cup, filling them about 3/4 of the way full.
Sprinkle cinnamon powder on top of each cup (optional).
Place the muffin tin into the air fryer and cook for 10-12 minutes, or until the pastry is golden brown and the filling is set.
Remove from the air fryer and let cool for a few minutes before serving.