David in Normandy writes
The only things that I find problematic to compost are whole brassica
stems, especially Brussels sprout. However, if these are coarsely
chopped first using a small hand axe then they rot fairly quickly too.

It doesn't really matter if the compost still has a few partially rotted
things in it when you come to use it (as long as you're not filling pots
with it) - so long as they're chopped to, say, 3 inches, so that they
don't make the compost difficult to dig out from the heap. If you don't
chop, you get long things all tangled up and stuck under a heavy lump
that you haven't yet dug out.
--
Kay