Melt the chocolate in a double boiler or in a pan over barely simmering water, stirring continuously. Transfer chocolate to medium bowl then quickly whisk in egg yolk, chilli and cream, whisking until smooth.
Place egg white in small bowl; beat until soft peaks form. Add sugar and beat until dissolved. Gently fold egg white mixture into chocolate mixture using spatula.
Spoon the mousse into two (250ml) glasses and chill in the fridge overnight. Serve topped with extra grated chocolate, if desired