Put the chocolate in a heatproof bowl. Heat the cream with the vanilla in a small pan until almost boiling then pour over the chocolate. Whisk until smooth and glossy. Leave to cool a little.
Whisk the egg white to soft peaks. Add the sugar and continue to whisk until stiff.
Fold the egg white into the chocolate mix then spoon into 4 individual serving dishes. Chill for 1 hour until set.
Use a large metal spoon or a spatula when folding in the egg white.