Preheat the oven to 220°C (200°C in a fan oven), 425°F, gas 7.
Make the custard: Place the sugar and plain flour into mixing bowl, 20 sec/speed 10.
Add the double cream, milk, egg yolks, lemon peel, and cinnamon stick, 20 sec/speed 4.
Transfer the custard into a saucepan and cook over medium heat, stirring continuously until it thickens. Let it cool.
Prep the puff pastry: Roll out the puff pastry on a floured surface. Roll up like a Swiss roll, then cut into 12 slices.
Use a rolling pin to flatten each slice into a round disc. Press them into the prepared muffin tin.
Fill each pastry case with the custard.
Brush the tops with the beaten egg.
Bake in the preheated oven for 15-20 minutes or until the pastry is golden brown and the custard is set.
Remove from the oven and let them cool before serving.
