[PJ-Comix]

I thought it would be a simple project to locate such a company that can provide molds in spherical sections but apparently none seem able to prove such molds despite their simplicity.

[Magnum44]

Silicon? No.

[Jonty30]

Size could be an issue. Silicon tend to be flimsy and the weight of a 12” cake could cause the batter to over flow the sides.

[William of Barsoom]

Why not a simple lightly eased metal mixing bowL? (Perhaps I’ve basically misunderstood the problem...) They’re cheap, and can be bought in stacked sets for varous diameters.)
Again, maybe I’ve missed the key point...

[yesthatjallen]

Best I can offer:

how to make molds for silicone casting

[Tucsonican]

I know a guy that does custom silicone molds but almost all of his stuff is more round and, well, I’m not so sure how they hold up at 400°F.

[PfromHoGro]

https://boldmaker.com/

?

[PLMerite]

[backpacker_c]

Even though this is a simple shape, you’re not likely going to be able to create it as 2 half spheres...

It’s simply going to take so much time for the core of the half sphere to get up to temp and baked, that the outer part that consist of the surface is going to be over baked.

You may have to create it as 4 different cuts of the sphere and then assemble the layers, which would allow for more even baking.