Roughly chop the chocolate and melt over a warm water bath. Mix chocolate and yoghurt. Whip the cream until stiff and allow the sugar to trickle in. Fold into the yoghurt
Finely chop the dark chocolate. Pour half the chocolate mousse into 8 small dessert glasses. Add the chopped dark chocolate, except for a little bit for sprinkling. Spread the rest of the chocolate mousse on top. Sprinkle with chopped chocolate and chill for about 1 hour.