Mix the flour and salt in a bowl and rub in chunks of the butter with your hands until they are slightly incorporated but there are still visible chunks in the mix. Mix in 1/4 cup (60ml) of the water and slowly add more as needed until the dough just comes together. Don't overmix. Wrap in cling film and chill in the fridge for 20-30 mins.

After chilling, roll the pastry out gently into a rectangle (about 20x50cm). You should still be able to see large flecks of butter in the dough at this point. Fold the top third of the pastry over and then fold the bottom third up over that so you have a business-letter fold. Turn the dough 90º (left or right) and roll out again. Fold in the same way as before and turn 90º again. Roll out, fold and turn twice more, then wrap in the cling film again and allow to chill in the fridge for another 20 mins.

After chilling, roll out the pastry into a large rectangle (about 30x45cm) and roll the dough up lengthways (it should look like a really long sausage shape). Slice the dough into 24 circles (there should be a faint spiral in each circle). Gently roll out the circle until wide enough to be pressed carefully into two greased 12-hole muffin tins (if you only have one, make 2 batches). Chill the tins of pastry cases in the fridge and preheat the oven to 220C/425F/gas 7 while you make the custard filling.

First, make a syrup by boiling the water with the xylitol, cinnamon and lemon peel (if using). Boil for 5 mins, until reduced by half. Remove the peel, pour into a cold bowl and allow to cool while you whisk the eggs, egg yolks and cornflour together in a separate bowl or large jug.

Bring the milk to just under the boil in a large saucepan. Just as you start to see a few bubbles and the milk is nice and hot, pour it very slowly into the egg and cornflour mixture, whisking all the time, until everything is smooth and combined. Pour the whole thing back into the saucepan and return to a low-medium heat, allowing to simmer for 2-3 mins until the custard just starts to thicken slightly.

Remove from the heat and pour in the vanilla extract and the cooled syrup, whisking continuously until thickened. Spoon or pour the custard mixture into the chilled pastry cases. Bake in the preheated oven for 12-18 mins, until the custard is just set, the pastry is golden and the tops of the tarts are starting to catch and blacken in places. Allow to cool completely and dust with ground cinnamon before serving warm or cold.