For the syrup, bring the water, sugar, cinnamon stick and lemon zest to the boil, then boil for 3 minutes. Remove the cinnamon and zest.

Whisk the flour into 100 ml of cold milk. Heat the rest of the milk, pour it onto the flour while whisking, return to the pan and thicken for 2 minutes over a medium heat, whisking constantly.

Pour the hot syrup in a thin stream onto the custard while whisking, leave to cool for 15 minutes, then whisk in the egg yolks and strain.

Roll the puff pastry into a tight log and cut it into 12 slices. Lay each slice flat in a buttered tin and press it out with a wet thumb, from the centre to the edges, until it comes slightly above the rim.

Preheat the oven to its maximum, 250 to 280 °C, with the baking tray inside. Fill the tins three-quarters full with custard.

Bake for 12 to 15 minutes at the top of the oven, until the pastry is golden and the custard speckled with brown. Leave to cool slightly and serve dusted with cinnamon and icing sugar.