Preheat the oven to 475°F (245°C). Gently heat the milk with 2 to 3 strips of lemon zest and the cinnamon stick to a simmer, then remove the lemon and cinnamon.

Mix the flour with a little of the milk to a smooth paste, then stir in the rest of the milk. Return to the heat, whisking constantly for a few minutes until thick.

Place the sugar and water in a saucepan, stirring until the sugar has dissolved. Bring to a boil and allow to boil for 3 minutes, then whisk into the milk mixture.

Place the egg yolks in a bowl and slowly add the milk mixture, whisking constantly. Transfer to a jug and allow to cool slightly.

Lightly butter all the holes in a 12-hole muffin tin. Roll the pastry out into a rough rectangle, then roll each rectangle up from the bottom to the top. Cut each roll into 12 discs. Place one disc flat into the base of each muffin hole, then, with wet thumbs, gently press out until the pastry comes about half way up each hole.

Pour the custard into the pastry cases, then bake for about 15 minutes, until set and caramelized. Sprinkle with sugar and cinnamon, then serve while still warm.