How Old is Gâteau Basque?

Very hard to say, reader Don. Obviously this version has baking powder in it, which would make it a relatively recent invention. Yet somehow I have a feeling that chemical leavening only came to gâteau Basque this past century. Unleavened, yet still sweetened and enriched versions probably go back a few hundred years, and unsweetened pie-like versions probably date to the Middle Ages.