Prep. time: 15 minutes
Cooking time: 20 minutes
Cooling time: 4 hours

 For a professional look, dust the top of the pie with powdered cocoa.

Another suggestion: once the mousse is set, cover it with a thin layer of ganache.

Tip
If you're not used to melting chocolate in the microwave, start with just 30 seconds. If the chocolate is almost melted, simply stir it. Otherwise, continue in 30 second intervals because it will seize easily if overheated. 

Substitute
You can substitute graham crumbs or speculoos crumbs for the pastry. Whir in a blender for 10 seconds and combine with 30 g melted butter. Press the mixture into the pan and bake for 10 minutes. 

Preheat the oven to 200 °C / 400 °F.
Pastry

1. Combine the dry ingredients (flour, salt and sugar) with a fork. 
2. Cut the butter into the dry ingredients with a pastry cutter or a fork until the mixture is sandy. Avoid using your hands, which would warm the mixture and make the pastry tougher. Finally mix in the vinegar. 
3. Line the bottom of a 12 cm non-stick springform pan with pastry. 
4. Bake for 15-20 minutes until the pastry begins to turn golden. Remove from the oven and cool. 

Filling

1. Chop the chocolate finely and melt in a double boiler or microwave. Cool to lukewarm. 
2. Whip the cream with the sugar.
3. In a separate bowl, beat the egg white to soft peaks. 
4. Gently whisk the chocolate into the cream; add the egg yolks; finally fold in the egg whites gently to prevent the mixture from deflating. 
5. Pour onto the crust. 
6. Refirigerate at least 4 hours before unmolding.