Late last year Our Nerd Home published a useful guide on how to make your own chocolate RPG dice. You needed some dice, silicone mold and chocolate.
The ONH team have a walk through that even I would attempt. Grab some Silicone stuff from Amazon, wrap your d20 in it but leave a hole you can pop the dice out once the silicone sets. That gives you the mold. Then pour in some melted chocolate, let that cool and then pop out the chocolate.
Once you’ve mastered the art of making tasty d20s you can move on to more awkward shapes.