Sweet sweet Friday: White Chocolate Plum Mousse Cake

I don't know much about parenting but I have learned in the last 18 months that it's not a good idea to attempt complicated kitchen manoeuvres when the Small Girl is awake. So I don't know what came over me a couple of Saturdays ago, when I decided to make a cake I'd spotted in Cuisine magazine for a dinner party we were going to that night. The Boy Wonder was hanging around, having breakfast and reading the paper, and I figured he and the Small Girl could amuse themselves while I played happily on the other side of the island.
They both have an unerring talent for choosing their moments to really need me when I really need them to be not needing me, if you get my drift - and so I made more than a few cock-ups along the way because I wasn't concentrating on the task at hand. But even though I fretted about it all the way to the party, this cake was a winner. Six adults demolished it in seconds and hailed me as some kind of kitchen genius. Perhaps I should cook with the Small Girl around more often.

White Chocolate and Black Plum Cake
This cake, which I have adapted from one by Ginny Grant in the September 2010 issue of Cuisine, is like a softly set mousse. It contains no flour, making it ideal for the gluten-intolerant.
It might look a little flat when you turn it out of the tin, but the incredible combination of lightness and richness soon makes up for that. Good with a generous dollop of whipped cream (who says your thighs need to have a gap between them?)
Black Doris Plums are a very New Zealand ingredient - the sort of thing that you can't buy from orchards any more, only in tins. If you can't find a suitable plum to substitute, I suggest trying tinned apricots.

850g can Black Doris plums (a dark purple plum, similar to an Omega), drained, halved and stones removed
250g good quality white chocolate
150g butter
150g caster sugar
4 eggs
zest and juice of one orange

Preheat the oven to 120C. Line a 22cm round cake tin with baking paper and grease with butter. Line a large roasting dish (big enough to hold the cake tin and around 5cm deep) with a tea towel and put the prepared cake tin on top.
Place the plums in the prepared cake tin, cut side down. Set aside while you make the batter.
Place the chocolate and butter in an ovenproof bowl and put in the low oven to melt. Keep an eye on it - about five-10 minutes should be enough. Remove from the oven.
In the meantime, put the orange juice into a measuring cup and top it up with water if necessary to reach 75mls. Pour this into a small saucepan and add 100g of the sugar. Heat until the sugar has dissolved and the syrup has come to the boil. Remove from the heat and let cool for a few minutes, then add this to the chocolate and butter mixture.
Beat the eggs with the remaining 50g of sugar until very light and fluffy. Pour in the chocolate mixture and beat until just combined. Carefully pour this batter over the plums in the prepared cake tin.
Pour just-boiled water from the kettle into the roasting dish (that the cake tin is sitting in) until it comes halfway up the sides of the tin. Carefully put this in the oven and bake for 50 minutes, or until the cake has just set. Let cool in the water bath before turning out onto a plate. If you're making this in advance (which is advisable, unless your guests are fine with being ignored for about half an hour), then put the cake in the fridge and turn it out just before serving.

Do you have a favourite end of the week baking treat? Add it in here to spread the sweetness of Fridays...