L'Opera Cake Geometry

The famous l'opera gateau is not exactly unrelated to my Paris trip. I keep staring at my rectangular suitcase

and thinking about pastry geometrie instead of packing.
 

I tried opera cake at Sadaharu Aoki's patisserie

on 35, rue de Vaugirard, 75006
Sadly, I cannot report how it tasted.

I was too busy admiring it's perfect architecture and lovely dimensions.

The cake was first created by Louis Clichy in 1903.
But Dalloyau renamed it after the grand Paris Opera
and is reknown for their version. I stole a shot at Galerie Lafayette Gourmet.

Every French patisserie makes a version of this popular multi-layered chocolate decadence.
L'Epicerie has their monster versions...I would love to figure out why a squared cake in the US connotes an
office party birthday or a banana cake?
Where is the panache?
Where's the ganache? Humm.

Pierre Herme makes what looks like an opera cake but he changes the equation.
Called the Carrement Chocolat, it is not layered.
Inside is:
(biscuit "molleux chocolat", creme onctueuse au chocolat, mousse au chocolat, fine feuilles de chocolat craquant)
Well I see the word feuille / leaves, so maybe it is layered?
Help me out here.

I brought the petit four version home to paint.

There's nothing like the challenge of painting a square
on a rectangular piece of paper.But I think I forgot to taste it...
Uh ohThese (20!) step-by-step demo pictures are from

the Meilleur du Chef.dom..
Here's what's inside the cake:
Giaconda biscuit
Coffee syrup
Coffee buttercream
Chocolate ganache
Chocolate glaze
Not exactly "a piece of cake" to make!
I think I better focus on the 20+ layers going inside my little suitcase...ahem