Ham, of course. It's always been the Yule Boar here in the North. I don't know where the heck Christmas turkey comes from?
http://www.orkneyjar.com/tradition/yule/yule4.htm
"Pork is a traditional Yule dish in Norway - probably a reminder of the time when the boar, an animal sacred to Freyr, the Norse god of Yule and fertility, was sacrificed at Yule and its flesh eaten as part of the feast."