• Melt the chocolate in a bowl set over a pan of simmering water (bain-marie) and leave it to cool slightly, without letting it set.
• Whisk the egg whites to stiff peaks and set aside.
• Whip the cream to soft peaks and set aside.
• Whisk the egg yolks and sugar until pale, thick and fluffy. Keep whisking until the sugar grains have dissolved and the mixture is almost white – this easily takes 4-5 minutes.
• Fold the chocolate into the egg yolk mixture, then fold in the whipped cream.
• Finally, fold the egg whites into the chocolate mousse, stirring gently until the texture and colour are even – do this in a couple of batches if you prefer.
• Pour the chocolate mousse straight into a serving bowl or individual bowls, or transfer it to a piping bag if that is easier and pipe it into small glasses. If you like, smooth the tops with the back of a warm, dry spoon.
• Chill the chocolate mousse until ready to serve – ideally for a couple of hours or overnight.

Crystallised chocolate

• Bring the water and sugar to the boil in a small saucepan and cook until the syrup reaches about 135°C (use a sugar thermometer).
• Turn off the heat and pour the chopped chocolate into the syrup while whisking with a hand mixer – the chocolate will quickly form small "crystals".
• Tip the crystallised chocolate onto a sheet of baking parchment and leave to cool.
• Serve the chocolate mousse topped with crystallised chocolate, chocolate shavings and gold flakes.