I have made the gateau before - several times. Here’s some photos of a previous iteration, and here is a link to the crepe recipe I use. A single batch will make a modest cake, but I like to double it for larger crepes, more of them, and thus a great big gateau. 
It’s super easy to make and everything can be made in advance. I usually mix the crepe batter the night before (using a blender and then chill overnight), making the crepes the next morning. They can sit all day (covered, once cooled). The bechamel also can be made in advance, so at dinner time, it’s just assemble and bake. Holds up well - we love the leftovers reheated.
