When I was making Nigella's Chocolate Orange Mousse I melted the dark chocolate and tried to loosen it with a third of the cream mixture but it just all seized up and went very thick which meant I couldn't fold it into remaining cream mixture. I had left the chocolate to cool first. What could have gone wrong and how do I avoid this next time? Thanks
Nigella's Instant Chocolate Orange Mousse is as mixture of melted dark (bittersweet) chocolate, condensed milk and whipped cream flavoured with orange juice and zest. The whipped cream and condensed milk are folded into the melted and cooled chocolate.
The chocolate in your mixture could have siezed - this is where the chocolate turns grainy and thick and may look slightly oily or greasy when it is stirred. This usually happens if a little water comes into contact with the chocolate while it is melting and often it is from steam in the pan of hot water below. When you remove the bowl from the pan of water do it carefully and quickly dry the base of the bowl with a tea towel.
Chocolate can also burn very easily and again goes grainy and thick when stirred. It is very possible that this happened instead. When melting chocolate over a saucepan of hot water make sure that the bowl doesn't touch the water, stir regularly and remeove the bowl while there are still some small lumps of unmelted chocolate in the mixture. They will melt in the residual heat of the already melted chocolate. If using a microwave then do so very carefully, using 10 second bursts of power and stirring between each burst. Again, stop heating the mixture while there are still a few small lumps of unmelted chocolate left to prevent it from overheating.