Yeah. The photo compositions can be somewhat… dreamy. After some thought, I'm starting to think the banana millefeuille is not intended to contain the walnut/hazelnut nougatine. Reason being the walnut nougatine made in the appendix is quite coarse, whereas the caramelized pâte sablée is very fine textured so as to be workable into thin sheets—these two textures don't seem to go together. Still, walnut does sound like a nice pairing/enhancement with banana—it's just that the walnut nougatine would just have to be laboriously re-ground quite finely before mixing it in, and I don't think the recipe meant to do anything like that. Another big clue is in the nearly identical peanut millefeuille recipe on the following pages (pp 188-189), mentioning the exact same nougatine in the ingredients. It seems random and arbitrary to introduce walnut/hazelnut flavors into what's predominantly a peanut dessert, in this context. And since the online recipe written in French doesn't use it, I'm inclined to guess it's a typo.