Steps
1. Melt the dark chocolate in a microwave or over a double boiler until smooth.
2. In a separate bowl, whip the heavy cream with sugar until soft peaks form.
3. Fold the melted chocolate into the whipped cream gently until well combined.
4. In a small glass or dessert bowl, break the biscuit into pieces and layer it at the bottom.
5. Spoon half of the chocolate mousse over the biscuit layer.
6. Repeat the layering with the remaining biscuit and mousse.
7. Refrigerate for at least 30 minutes to set.
8. Before serving, dust with cocoa powder for garnish.