Where can I get the best whole chocolate cake?

My mother absolutely loves chocolate cake. The chocolatier, the better. She doesn’t eat much of it these days, but she has a big birthday next week and I’d like to get her a delicious fancy chocolate bomb of a cake to show her how much she’s loved.

What place would you recommend? I’m looking for probably an 8" one-layer cake, ideally from a bakery in the south bay (Mountain View, San Jose), but the whole peninsula is in play. Money isn’t really an issue as far as this purchase is concerned.

Thank you!

Maison Alyzee has a Valrhona that’s good. See the pictures in the link.

Not sure if Mademoiselle Collette, which has a branch in Palo Alto, has chocolate cakes. But Collette, along with Alyzee, are my favorites for fancier pastries, even though they are very pricey.