From mojewypieki.com.  I like Jaffa cakes,  but this recipe I had to try- the chocolate mousse on top and fresh orange in the orange jelly must have been money. :-).

I made the sponge the usual way, 4 eggs, 4 tbsp of plain flour, 2 tbps of potato flour, a tsp of baking powder all for a large sponge. When cooled, 2 orange jellies went on, but made with 750 ml of water, not with 1 l, as the packets suggested. The jelly was already in the process of setting when I poured it onto the sponge layered with chunks of fresh orange- what a lovely treat, next time I’ll use even more.  I left it all overnight to set and then made the mousse. 200 g of dark chocolate melted above boiling water with 30 g of butter, 3 tbsps of orange juice. 3 eggs, separated, whites whipped with 50 g of sugar, yolks slowly added to the chocolate mixture and whisked in. When the whites are ready, half of them go into the chocolate mix to loosen it, then also 100 ml of double cream, whipped. And the rest of the egg whites.  All this sets in the fridge overnight and right before serving, a generous sprinkle of cocoa goes on top. Excellent. 🙂