A one egg sponge makes enough for four portions and self control is weak where cake is concerned!.
I found this recipe
I reduced it down to a tenth (which was easier than you'd think), followed the instructions apart from greasing the baking dish and dusting with icing sugar and I put some stewed plums (and syrup) in the bottom before piling on the batter. I won't go into any details as all the info is through the link.
Using the syrup as well as the halved and stewed plums made a lovely, sticky, toffee-ish sauce around the side.