In a heat-proof bowl suspended over a saucepan of simmering water, add Dark Chocolate (400 gram). Cook, stirring occasionally, until the chocolate is melted and smooth.
Remove the chocolate from the heat and allow to stand for 10 minutes.
In a mixing bowl, add Chocolate Biscuits (200 gram) and Butter (100 gram). Stir together until mixture has the appearance of wet sand.
Transfer the biscuit and butter mixture to a greased 20-centimeter springform tin lined with non-stick baking paper. Press down with a flat-bottomed glass until even. Place into fridge to chill for 30 minutes.
In a mixing bowl, add Thickened Cream (600 milliliter) and Vanilla Extract (2 teaspoon). Using an electric mixer, beat until mixture forms soft peaks.
Gently fold the cream into the cooled chocolate, a bit at a time.
Transfer the mousse into the cake tin. Smooth the surface with a spatula. Place in fridge to chill for 3-4 hours, or until set.
Garnish with Milk Chocolate (to taste). Transfer to serving plate. Enjoy!