Sift the flour, cocoa powder and icing sugar into a bowl.
215 g plain flour (all-purpose flour), 35 g cocoa powder, 2 tbsp icing sugar
Rub in the butter until it looks like fine breadcrumbs.
125 g butter
Beat the egg yolk with the cold water then pour it into a well in the middle of the flour mixture.
1 egg yolk, 4 tbsp cold water
Use a spoon to mix it together and then press together with your hands.
Cover with clingfilm and put it in the fridge for half an hour to chill.
Remove from the fridge and roll out carefully so it is larger than your tart tin. Drape over the tin and push the corners gently into place. Press the pastry round the tin so the edges become fluted.
Trim off the edges with a sharp knife, to the shape of the tin.
Place your tin on a baking sheet to make it easier to handle.
Then put the tin (still on the sheet) back into the fridge to chill for another half an hour. Meanwhile preheat the oven to 180℃ / 350℉.
Remove the pastry shell from the fridge. Prick the base with a fork to stop it rising as it bake and to allow the steam to escape.
Fill the pastry shell with baking beans (I use dried pasta, you can also use dried rice) on top of baking paper and bake for 10 minutes. Then remove the baking beans and baking paper and bake for a further 10 minutes for the base to become crisp.
Leave the case to cool.