I have seen recipes require ground star anise.

Do you grind the shell or the actual seeds or both?  Is the flavour not just in the husk?

For any recipe that states using ground star anise, I would in fact use aniseed instead it has a better flavour. Star anise is better used in liquids.

Makes sense - I have never ground them up. I do like to suck the juices out of them though and tend to leave them in the finished meal.