I found the original mold and thought it was a great idea. I didn't like the blank back, so I mirrored the design side and joined the two with a hinge. I printed this without supports and at 0.1 layer hieght. It worked perfectly right of the plate.

I'll probably make one in resin too for a smoother appearance.

EDIT: 11/22/2021 - Added blank mold by request. Could be cleaner, but I think it should work.

EDIT: 04/12/2022 - Added a spout version for a resin request. No idea how it will turn out, but it's available.