Melt 200g dark chocolate in a basin set over a pan of simmering water and let cool for a few minutes. Whip 600ml double cream
until it forms soft peaks, then fold a couple of Tbs of this into the chocolate and mix gently. When this has been incorporated,
spoon the chocolate mixture into the whipped cream, folding gently until it is all combined and smooth and glossy. Spoon into glass
serving dishes and chill for a couple of hours, until set. Meanwhile, melt a couple of Tbs orange marmalade with a little warm water
until runny, then let cool. To serve, top the mousse with a dollop of crème fraîche followed by a spoon of the orange sauce.