Preheat oven to 180°C (350°F).
Rub butter into flour and sugar until mixture resembles breadcrumbs.
Add egg yolk and cold water to form a dough, chill for 20 minutes.
Roll out dough and line 6 tartlet tins, prick bases with a fork.
Bake for 15–20 minutes until golden, then cool completely.
Heat cream until just boiling and pour over chopped white chocolate, stir until smooth.
Add vanilla extract to ganache and let it cool slightly.
Fill tartlet shells with white chocolate ganache.
Arrange fresh raspberries on top of each tartlet.
Chill for at least 30 minutes before serving.