Rub the flour, sugar, and butter together with your fingertips until the mixture resembles fine breadcrumbs. Mix the egg yolk with a little cold water, then add to the bowl and bring together to form a dough. Wrap in clingfilm and chill for 30 minutes. Line a tin with greaseproof paper strips, this will help you lift out your custard tarts easily.
Roll out the chilled dough on a lightly floured surface. Cut out 9-12 circles and press them gently into a cupcake tin. Chill again while you prepare the custard.
Warm the milk until just lukewarm (do not boil). In a bowl, whisk the egg yolks, vanilla and sugar until pale, then gradually whisk in the warm milk. Strain the mixture into a jug.
Carefully pour the custard into the pastry cases. Preheat your oven to Gas mark 6/180C Fan/200C/400F and bake for 15 minutes, then reduce the oven temperature to Gas mark 4/160C Fan/180C/350F and bake for a further 10 minutes, until the custard is just set, lightly golden, and slightly puffed.
Leave the tarts to cool in the tin for 1 hour. Use the greaseproof paper strips to carefully lift them out.
Decorate with orange-coloured melted white chocolate and edible eyes to create chick designs ( I recommend using white chocolate to attach the eyes, instead of pressing the edible eyes in as it will make your custard crack). Store in the fridge and consume within 2 days.
