I live in Brittany. I very rarely cook cakes, but I sometimes do far breton. In fact it is a sort of eggy, sweet Yorkshire pudding. Prunes are very common, but you can use apples (aux pommes), or nothing (nature). Bretons wouldn't use brandy essence. They would use apple brandy (lambig), known in England as Calvados. Failing that any spirit - brandy, whisky, vodka, grappa etc. Often tea is used to soak the prunes.