For the chocolate cream, crumble the chocolate into a saucepan. Add the orange zest, orange juice and butter and melt the chocolate in a water bath while stirring.
When the chocolate has melted, remove the pot from the water bath and mix the liqueur or cognac into the chocolate. Allow the chocolate to cool slightly.
In the meantime, whisk the egg yolks in a bowl until well frothy. Add the (room-warm) chocolate mixture to the egg, stirring constantly. Beat the egg whites until stiff and fold into the chocolate cream. Then pour the chocolate cream into small bowls and place in the refrigerator for two hours.