What materials would work for a waffle iron?
Aluminum is easy to CNC mill and it can be make non-stick

It needs to be finished to a semi-gloss, and have a slightly undulating (smooth wave pattern) surface to allow for release

It should be hard-anodized to reduce surface pores and future oxidation. Do not scrub hard-anodized surfaces, just soak

Cast aluminum will most likely have too many surface pores to me useful