In a letter to Cassandra Austen dated 18th December 1798, immediately after Jane Austen's 23rd birthday, she made passing reference to her birthday.
I'd like to invite you all today to join me in a celebration of Jane Austen's birthday, but in my opinion a dish of Tea alone will not suffice. This great lady deserves a birthday cake, though such a thing was not common practice at the time. However, as she wrote in a letter in 1808,
The purchase of prepared food, especially cakes, would have been rare indeed for a family of women of limited means, and most baking would have been made at home.
The term "sponge" had only recently begun to be applied to a light-textured cake. As Maggie Lane in Jane Austen and Food tells us,
...she referred, of course, not to the Victoria sandwich we often call sponge but to the true fatless sponge-cake, made with just flour, eggs and sugar. Raising powder was not available before the 1850s, so the lightness of a sponge had to come from the amount of air that could be beaten into the mixture. Fortunately, labour was cheap and uncomplaining.
Since a good sponge-cake, according to Hannah Glasse in 1747, should be beaten for an hour, it's not hard to see why the purchase of such a cake, without the repetitive strain-inducing labour, should be such a pleasant prospect.
Here, then, is a recipe for a sponge-cake from Maria Eliza Rundell's 1806 book, A New System of Domestic Cookery.