Combine flour, salt and sugar in a food processor. Add the butter and process until the mixture resembles coarse breadcrumbs.
With the machine running, add the ice water slowly and in a steady stream. Process until the dough holds together without being wet or sticky. Do not process for more than 30 seconds as the dough will be tough.
Divide the dough into two equal halves. Flatten each half into a disc and wrap in cling wrap. Refrigerate for at least 1 hour.
Preheat oven to 180°C.
Butter and line 6 mini pie tins with baking paper (you may have leftover dough and filling to make a few more tarts). On a lightly floured surface, roll out the dough. Using a wide cookie cutter or wide-rimmed glass, cut circles out of the dough.
Line the pie tins with the dough. Using a fork, make a few holes in the base to allow airflow. Wrap the pie tins in cling wrap and refrigerate for 30 minutes.
Remove cling wrap from tins. Blind bake the tarts using dried beans or pie weights for 10-15 minutes, until golden.
Remove from the oven and cool completely.
Bring the milk, 50g sugar and the vanilla bean to the boil over medium heat in a heavy-based saucepan.
In another bowl, whisk the yolks and remaining sugar together, then gradually fold in the cornflour. Carefully pour small amounts of boiled milk into the yolk mixture, whisking as you pour. Continue until you have used approximately half the milk.
Bring the remaining milk to the boil. Remove the vanilla bean and carefully whisk in the yolk mixture. Continue mixing the thickened mixture until it returns to the boil.
Transfer to a clean, dry bowl and cover with cling wrap. Let it cool then refrigerate until required.
When ready to serve, fill the mini tarts with custard and decorate with sliced strawberries or raspberries, if desired. Refrigerate for 15 minutes before serving.