Use a coarse box grater to grate chocolate for decorating. Pie can be made up to one day ahead. Store in an airtight container in the fridge.
220g packet frozen sweet pie case
1 tablespoon caster sugar
Finely grated dark chocolate, to decorate
1 egg yolk
2 tablespoons caster sugar
1 teaspoon vanilla extract
1 tablespoon cocoa powder
1 cup store-bought chocolate-flavoured milk
300ml tub thickened cream
Place frozen pie case in foil tray on an oven tray.
Cook in a moderately slow oven (160C) for about 12 minutes, or until light golden.
Meanwhile, make filling. Whisk eggs, yolk, sugar, vanilla and sifted cocoa in a medium jug until sugar is dissolved. Add milk and ¼ cup of the cream, returning remaining cream to fridge. Whisk well.
Open oven and partially slide out shelf. Pour filling into case. Gently slide shelf back in. Close door. Continue to cook for about 40 minutes, or until just set. Custard should still have a slight wobble in the centre. Remove from oven. Cool to room temperature. Refrigerate until cold.
Beat remaining cream with sugar in a small bowl of an electric mixer until soft peaks form.
Just before serving, remove pie from foil tray. Spoon over cream. Sprinkle with chocolate.