Hull and cut strawberries in half, put into a dish and sprinkle over caster sugar to macerate for 30 minutes or so.
Make some crème patissiere, as follows. Whisk 3 egg yolks with 50 g caster sugar until pale golden, then whisk in
a Tbs plain flour and a Tbs cornflour. Warm 250 ml whole milk and pour this into the egg mixture, whisking until
combined. Stir in a tsp vanilla extract and pour the whole lot back into the saucepan used to warm the milk.
Gently heat the custard to a simmer, stirring all the while, until thickened and smooth. Transfer to a bowl,
cover with cling film to prevent a skin forming, and chill in the refrigerator for half an hour. Meanwhile,
unroll a sheet of puff pastry onto a lined baking sheet. Cut 2 cm wide strips from the edges. Moisten the edges
of the remaining sheet with water and gently press on the strips around the edges, to build up a little wall.
Prick the centre of the pastry all over with a fork, sprinkle granulated sugar onto the walls around the edge
and bake in a 200°C oven for about 20 minutes, until puffed up and golden. Remove from the oven and let cool,
pressing down the middle with a spoon. When cool spread the crème pat onto the pastry shell and cover with
the macerated strawberries and their juices.