It looked so easy! And I suppose it should be, but, this is where it becomes evident that I am only a novice cook.
There is a technique to melting chocolate, which Nigella doesn't go into in her recipe. TWO key points:
FIRST: the operative words are GENTLY and SLOWLY. And you only need the chocolate there for a short while. My flame, which I thought was low, was probably too high, and I left the chocolate there for too long. So instead of melting, it started to get lumpy and grainy. I later read that what was happening was that the chocolate was beginning to "scorch". What I should have done was to add some vegetable oil or shortening. Instead, I decided to pour in a little bit more water. Which leads me to the second point,
TWO: Chocolate HATES water and if you want to melt your chocolate with other ingredients, including water, you have to add the water at the start of the process and in the correct proportions. NEVER EVER add it while you are melting it. The chocolate will "seize" - separate and clump. Which was a process I observed first hand...
Still blissfully unaware of the disaster at hand, I thought, perhaps the chocolate just needed to be folded into the cream.
Here is where I committed error number three. The cream was to be whipped till thick. But I think I overwhipped it. Well, it didn't look overwhipped, in fact, it looked perfect. But once I poured it into the chocolate and started mixing it in, the mixing process tipped the cream over the "overwhipped" edge and it started separating!
This was when I realised that my chocolate mousse didn't look anything like mousse. It looked just like oily chocolate clumps. I miserably ladled the chocolate mixture into glasses, hoping for the best, but realising that it was definitely not going to look like Nigella's beautiful mousse.
In the end, the chocolate mixture didn't look or taste anything like mousse. But, surprisingly, it wasn't all ruined. It was still edible, and because of the marshmallow, didn't harden into a rock of chocolate. And since I used good chocolate, I could still nibble on it to fulfill my chocolate craving.
I have since learnt how to melt chocolate (see this very useful video, and article) and I can't wait to try out the recipe again.