Preheat your oven to 550°F (290°C), and lightly grease a 12-cup muffin tin.
In a saucepan, bring to a boil the sugar, water, vanilla extract, lemon peel, and cinnamon stick. Cook until a thermometer reads a temperature of 220°F (100°C) which is the thread stage. Do not stir!
In a bowl, whisk the milk, flour, and salt together very thoroughly. Cook over medium heat, whis constantly for 5 minutes or until well combined and thickened. Let cool for 10 minutes.
Next, whisk in the egg yolks, the followed by the sugar syrup, first discarding the cinnamon stick and peel). Mix until everything is well-combined. Strain the custard and set aside.
Cut the puff pastry sheet into two pieces and place them on top of each other. With the short side facing yoiu, tightly roll the sheets into a log. Cut the log into 12 evenly sized slices.
Place one slice in each of the muffin tin. Regularly dipping your thumb in cold water first, press down into the center of the dough piece and press outwards to form a cup. The cup should be just above the top of the well of the muffin tin.
Fill each pastry cup 3/4 of the way to the top with custard.
Put the tray in the oven and bake for 10-12 minutes, or until the custard starts to caramelize and blister and the pastry turns golden.
Serve warm, with powdered sugar and/or ground cinnamon.
Portuguese Custard Tarts ( Pasteis de Nata) https://cultureatz.com/how-to-make-custard-tarts-portuguese-pasteis-de-nata/