The recipe is from Nigella Express, which was one of my Christmas pressies (thanks Mr Cake!), though I've actually made this dessert before, so I knew it was yummy in advance. ;-)
It's not quite instant, but it only takes a few minutes to whip up, and then perhaps an hour to cool and set up nicely. You just melt chocolate and marshmallows with a little butter and hot water - into a delicious chocolatey soup. I used only the white marshmallows (since the pink ones are faintly raspberry flavoured) but I doubt it would make much difference if you used both - but I happen to like eating the pink ones. ;-)
And then whip the cream and fold the chocolate through - just make sure you let the chocolate cool a little first (I may have done this a little too soon - it'll still work out fine but won't be quite as fluffy since the air will escape from the cream). Pretty simple, right? And it only takes one bowl and one saucepan - not four bowls, like my standard chocolate mousse.
Nigella claims this recipe serves 4-6, but we divided it six ways and I felt I still had a bit too much - and I'm definitely not a stingy dessert server - so I reckon you can make it go further.
Instant Chocolate Mousse (adapted from Nigella Express)
250g dark chocolate
60ml boiling water
1 tsp vanilla essence
Stir together the marshmallows, butter, chocolate and hot water over a low to medium heat. When smooth, transfer into another bowl to cool the mixture slightly.
Whip the cream with the vanilla intil thick, then fold in the cooled chocolate mixture. Spoon into bowls or glasses and chill for an hour before serving. Serves 6-8