Make the pastry and chill for 30 minutes in the fridge.
Line a tin with the pastry.
Preheat the oven 400F
Blind bake the tart case for 20 minutes.
Cream the fat and sugar for the filling.
Add cocoa gradually and stir.
Add the dry milk powder and water alternately until the mixture is the consistency of whipped cream.
Spoon the filling into the cool pastry case and refrigerate for 2 hours.
Cut and serve with squirty cream.