Lab diamonds are routinely grown in the shape of giant wafers. (And then smaller parts are cut out of the wafers.) This shouldn't be that hard to get if you really want it.

(I have a friend who used to have a job drawing cut plans for diamond wafers at Kyocera Unimerco.)

Hm, almost 5x the thermal conductivity of copper. Since this is HN.. let's say we were actually to build such a pan, is it practical?

My first thought is that the high conductivity doesn't necessarily mean it won't, being loose and hand-wavey with terminology because I don't know it, fracture with thermal shock, like non-borosilicate glassware (don't change the temp. too quickly) say, or ceramics (don't introduce too much of a temp. delta across the item, e.g. heating on a hob)?

Second thought is 'is it too much better than copper', in the sense that is the conductivity no longer the limiting factor? Copper is prized (and actually bloody hard to get these days - afaict everything on Amazon is copper-coloured or at best clad aluminium) because of fast 'response time' to change in heat, as you adjust the burner or pull it off the heat altogether. Conductivity also helps with even heating of course, but it doesn't help it cool particularly, which is limited by the rate of loss due to convection through air (and what's being cooked, which is what we want to limit if we're hoping for it to cool) and radiation?

Aren't diamonds quite brittle? I feel hitting banging the diamond pan against the burner slightly too hard will cause it to shatter. Or using a metal spatula too roughly.

Yes, they are.

I assume that wouldn't be as aggressive as tempered glass or something, but it's funny to imagine your pan shattering followed by every other piece of glass/ceramic in the room when the fragments hit them.