Mix the butter, diced, and the icing sugar with a wooden spoon. Incorporate the egg, beaten, then add the flour until you have obtained a homogeneous dough. Wrap in cling film (plastic wrap) and keep in a cool place for at least 1 hour.
Roll out the pastry on a worktop and line a greased mould with it.
FOR THE FILLING:
Pre-heat the oven to 180°C (350°F).
In a large saucepan, bring to the boil the milk with the vanilla pod, split in two and seeds scraped into the pan, as well as 50 g (13/4 oz) of sugar.
In a large mixing bowl, whip the eggs with the yolks, cornflour and remaining sugar until the mix whitens. Pour the hot milk over it, stirring constantly, followed by the cream.
Pour everything into a saucepan and put over a low heat, whisking non-stop until the cream thickens and starts to boil. Remove the vanilla pod and allow to cool away from the heat.
TO FINISH:
Pour the filling into it the pastry crust and smooth the surface. Bake for 50 minutes: the flan should brown nicely.
Remove from the oven and allow to cool down then refrigerate for at least 6 hours.