Turns out the day we were at Santosa, I gave them a call out of the blue, and they had room for us, so we went to l'Atelier. I naively assumed that we'd never be allowed in the real restaurant. But turns out the Atelier actually had a very good tasting menu ($200 with tax and stuff), so we took that. Honestly, it rivalled many fine restaurants we had eaten at:

It was an excellent dinner, we barely managed to get home from there :)
Now, the more interesting part is that I was talking with the French staff, and they told me that the main restaurant has a pretty lax dress code: no shoes, no shirt, no service :) (this is actually because weather in Singapore is truly unbearable and after 10mn outside you'll be drenched in sweat in your clothes, even at night).

So, we made plans to go back the next day for the restaurant and their even fancier tasting menu. It had flights of dishes that came in 3, and that was a very good idea (also sped up the service and turned a 4H+ dinner into a more manageable 2.5H one).
The menu was not any fancy molecular gastronomy, but it was a very good list of dishes, one after another. We were quite impressed:

we got some :)

this half foie gras half beef smoked was fantastic

room for cheese? :)

Then came time for dessert. It was painful by then :)

It was an excellent meal, and apparently cheaper than the Vegas location (although still a steep bill :) )