Instructions

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 zest, and cinnamon stick. Cook until a thermometer reads a temperature of 220°F (100°C). Resist the urge to stir!
Separately, whisk the milk, flour, and salt together very thoroughly. Cook over medium heat, whisking constantly, for about 5 minutes or until well combined and the milk is thickened. Take off the heat and let cool for 10 minutes.
Once cooled, whisk in the egg yolks. Then add the sugar syrup (first removing the cinnamon stick), and mix until everything is well-combined. Strain into a measuring jug.
Meanwhile, cut the puff pastry sheet into two pieces and place them on top of each other. Tightly roll the sheets into a log, from the short side. Next, cut the log into 12 evenly sized pieces.
Place one piece in each of the 12 wells of the muffin tin. Dipping your thumb in cold water first, press your thumb down into the center of the dough piece and press outwards to form a cup with the pastry. The pastry cup should have its top edge just above the top of the well of the muffin tin.
Fill each pastry cup ¾ of the way to the top with custard.
Put the tray in the oven and bake until the custard starts to caramelize and blister and the pastry goes golden brown (roughly 10-12 minutes).
Serve warm, with powdered sugar and ground cinnamon (both optional, but delicious)!