Easter Egg molds for resin, plaster and concrete. I recommend printing it in TPU, but I have also had success with PLA. It is best to brush the inside of the mold with household oil (such as that used for cooking) before casting. I've always got into the habit of pouring a small amount directly into the mold beforehand and then the concrete.

On my profile, you can find fitting easter bunnies to go with the theme.