Mmmm, the Gateau Basque is lovely. It’s not as hard as it sounds, I did mine over two days. Day one, make pastry cream and pate sucree dough. Day two, assemble and bake. And I remember that the technique of rolling the dough, draping it over the bottom of a turned-over pan, covering that with the springform, then flipping, worked very well. Just sounds complicated to describe. And there’s a change to the recipe, I’m sure you saw it in the post.
Any good quality cherries, jarred or jam, would be nice. My first pick would probably be the Fruit Perfect sour cherries in a jar (Rose recommends these in the cherry pie recipe), but the Crofter’s Morello is nice, too.
The rum in the pastry cream is a noticeable flavor (but not boozy), which can be good or bad, depending on your viewpoint.