We hope to construct a traditional Australian cake for friends when we visit the Harrogate area in May. Trouble is we need a plain unfilled sponge slab as the starting point. A prefilled sponge with jam and cream won't work. We can buy an unfilled slab in our supermarkets in Australia but need to know if we can in Yorkshire. And if not in a supermarket, would we be able to buy one in any bakeries. All help would be appreciated.