Another great recipe from Dorie Greenspan. It is a traditional dessert from the Pays Basque region of France with a double cookie-like crust and a custard, use recipe #405945, or jam filling. It's not overly sweet and can be enjoyed any time of day. It's very sturdy and therefore good for transporting. You can use different fillings like blueberry jam, sweet cranberry relish, or even lemon curd. This simple dessert is best plain or with a little whipped cream or ice cream. Doug requires at least 30 minutes to chill. Storing: Wrapped well, the jam-filled cake will keep for a day or so at room temperature. You can also keep the cream-filled cake overnight, but it will need to be refrigerated. However, because refrigeration can dry cakes. It's best to serve the cream-filled cake the day it is made.