I'm cooking for my father, who likes creme brulee and also likes
chocolate truffles, (Specifically, Cocoa Powder Dusted Truffles by
Truffettes de France.) and I'm trying to figure out a way to "combine"
the two.

Here's what I'm envisioning: Crème brûlée that is made the regular
way, but somehow top it with a layer of chocolate, then chill it.
When I remove the crème from the ramekin I'd then flip it, so that the
chocolate is now sitting on the bottom of the custard. Then of course
I'd torch the sugar on top, top with a single chocolate truffle, and
perhaps spoon a chocolate sauce of some sort around the custard on the
plate.

So here's my question: what sort of chocolate (recipe) would work to
achieve the above? Would mousse be too light, and get squashed by
the weight of the custard once flipped? Or is there some way of
getting that layer of chocolate to be a bit stronger than the
custard? Would just straight up melted chocolate pored into the top
of the ramekin work, letting it harden in the fridge?

And my second question: what sort of chocolate sauce do you think
would work nicely spooned around the perimeter of the dish?

(I executed Gordon Ramsay's Roasted Rhubard Crème brûlée dish and it
turned out quite well, so I had the inspiration to replace the rhubard
with chocolate and instead of jus de fraise, use chocolate. In case
anyone's wondering.)

Any suggestions or recommendations much appreciated!