Continuing my effort to deal with some of the very old word requests:
From what I can see, the spelling butty - already allowed in Chi - is used more often. Nevertheless, buttie is used quite often too, and given as an alternate spelling in a few dictionaries, as in the entry you quoted, Dave. So buttie will be accepted in Chi too from now on.
We currently allow the plural butties, since it is not the simple appending of an S to the singular butty. I think we should keep that as it is, since both forms of the singular are rare, but the form ending in Y is somewhat more common.
Butties are not generally spoken about in Australia, but I was interested to see that both buttie and butty appear quite a few times in New Zealand newspapers. For example, a 2012 article in the Otago Times, referring to the then Prime Minister, John Key, mentioned "the bacon buttie he purchased from the Lake Hawea Netball Club". And a Bay of Plenty Times article from September this year was headed, "Bus users enjoy bacon butties for car free day". The NZ word for sandwich that I'd previously noticed was sammy or sammie.
Incidentally, butty has another set of meanings from the English mining industry. It can be a workmate; a middleman negotiating between miners and the mine owner; or an unpowered freight barge intended to be towed. The word was used in some of these senses by D H Lawrence in several of his novels and stories.
