1. Melt the chocolate in a heatproof bowl set over a pan of simmering water (do not allow the
base of the bowl to touch the water).
2. Whisk the egg whites and lemon juice in a large, clean bowl until very frothy.
3. Add the sugar and continue to whisk until firm peaks form when the whisk is
removed.
4. When the chocolate has melted, remove the bowl from the heat. Whisk one-third of the egg
whites into the melted chocolate quickly and vigorously, until thick and well combined.
5. Fold the remaining egg whites into the chocolate mixture, using a spatula, until all of the
egg white has been completely incorporated into the chocolate.
6. Spoon the mousse mixture into four Martini glasses or four small ovenproof pudding
bowls or ramekins. Chill in the fridge for 2-3 hours, or until set.