- For the chocolate cream, whisk the sugar, cornstarch and salt in a medium saucepan. Whisk in the milk followed by the egg yolks and place the pot over just-higher-than-medium heat, whisking until it reaches a full simmer and becomes thick and glossy, about 6 minutes. Pour in the chocolate and butter and stir until melted. Stir in the vanilla. Transfer this mixture to a bowl and place a piece of plastic wrap directly on the surface of the filling to prevent a skin from forming. Cool the chocolate cream for about 90 minutes, until almost room temperature.
- Spoon the filling into the pie or tart shell and spread to level it. Chill for at least 4 hours to set.
- For the topping, whip the cream to a soft peak using electric beaters or a stand mixer fitted with the whip attachment, then whip in the icing sugar, skim milk powder and vanilla. Spread or pipe this topping over the chocolate cream and chill, uncovered, until ready to serve. The pie will keep after slicing, loosely covered, in the fridge for up to 2 days.