@Butter-Girl meals high in meat , seafood, some wholegrains if eating for the fiber & nutrients e.g spelt (ray said some of his teeth decayed from a time where he was eating a lot of wheat germ for the nutrients without calcium)

I boil for half an hour, then lay them out overnight on a tray, then bake tray at 90 C for 30 minutes.
I use a nutribullet pro blender. It turns it into fairly fine white powder.
I don't remove the membrane because most of my eggshells have been out for a while and the membrane dries stuck. I do recommend rinsing inside of eggshell after cracking so you get a cleaner powder later.