Weigh and sieve the flour and sugar together into a bowl
Add the butter and using your fingertips, mix together until you have fine bread crumbs
Add the egg yolk and mix together to form a dough.
Shape into a long fat sausage and rest in the fridge for half an hour.
Whisk together the sugar and cornflour then add the egg yolks and whisk until the mixture becomes pale and thickened. Set aside.
Pour the milk in to a pan, split the vanilla bean, scrape the seeds into the milk then add the pod. Bring to a simmer.
Slowly pour the milk into the egg yolk mixture in a thin stream while constantly beating.
Pour the mixture back into the saucepan and bring to a boil while whisking constantly, making sure to scrape down the sides.
Scrape the mixture into a bowl, cover with plastic wrap and chill until ready to use.
Weigh and mix the crumble ingredients together in another bowl to make a loose crumble.
To make the mince pies you’ll need a tray with 12 deep pie indentations in (the sort used for making cup cakes).
Brush each indent with some melted butter.
Take the pastry from the fridge and cut into disks, slightly larger than the diameter to allow for the depth of the cup cake tray. Each disk can be pushed into the indented tray. Aim to make it as thin as possible but not so thin you can see the tray through it. Patch any gaps with more pastry and trim around the top as neatly as possible.
Spoon a little of the custard in the bottom.
Then, fill each pastry case with the mincemeat filling to just a few millimetres below the top. Smooth down with the back of the spoon.
Sprinkle the streusel on top, allow to rest, ideally in the fridge, for about 10 minutes before baking. This is to prevent pastry shrinkage. Bake at 200°C for approximately 20 minutes [ideally on a baking stone] until the mince pies are golden brown.
Allow to cool for a few minutes then, using a small knife, carefully lift out onto a cooling rack.