I've made the Tropical Chocolate Cake twice and it was absolutely delicious but the frosting was difficult, I was mixing the icing for over an hour on the stove and it still didn't stiffen. It just would not work, so I ended up doing it in a normal mixing bowl, more like a regular meringue. What happened?
Nigella's Tropical Chocolate Cake (from FEAST) has a sponge cake that made with pineapple and slathered with a coconut-flavoured frosting. The frosting is a 7-minute (or Swiss meringue) frosting and is made by whisking egg whites and sugar in a bowl over a saucepan of simmering water. When the whites are whisked over hot water it helps the sugar to dissolve more easily and gives a firm and glossy meringue. The heat also helps to stabilise the meringue frosting so it will stand for longer. A meringue made from whisking egg whites and sugar together without any heat will start to deflate much more quickly.
There are several reasons why the meringue may not have thickened but the most likely is that the bowl was touching the hot water. If this happens then the whites can overheat and the meringue will not thicken. The other common reason for egg whites not whisking into a meringue is that there was some grease present. This can be from the bowl or beaters, so make sure that they are spotlessly clean and if in doubt wipe all of your equipment over with a piece of kitchen roll (paper towel) dipped into a little lemon juice. Also make sure that there are no traces of yolk in the egg white, as this will also prevent the whites from whisking properly.