Preheat the oven to 180°C/350°F/gas 4. Lightly grease a flan dish with a little butter.
In a large bowl, combine the rest of the butter with the flour. Rub together until it looks like a fine crumb.
Add the cocoa powder and icing sugar.
In a small bowl, beat the egg yolks together. Add the oil and 2 tbsp water.
Pour into the flour and butter mix to form a dough.
Lightly dust a clean surface with the flour and turn the dough out onto it.
Roll into an circular shape about an inch thick and place into your greased flan dish.
Prick the base with a fork and allow to chill in the fridge for 30 minutes.
Remove from the fridge and fill with baking beans. Place in the oven for 20 minutes until set. Allow to cool.
In the meantime you can make the filling. Gently melt the chocolate in the microwave on 30 second blasts.
When melted pour in the vanilla extract and the milk. Add two tbsp of water to thin down the chocolate if needed. Add the crème fraiche to the chocolate.
In a large bowl, whisk the egg whites to stiff peaks and add the sugar. Fold into the melted chocolate mix until evenly mixed.
Before you put the filling into your pastry base, remove it from the flan tin. Pour in the filling and smooth with the back of a spoon.
Place in the fridge overnight to set.
Garnish with icing sugar before serving.