Sugar crystals pressed between two slices of (usually buttered white) bread. Known by this name at least since an article in the 'Glossop Record' on Saturday 19 June 1869 which complains of churchmen whining "like children who have lost their sugar-butties." Sugar Butties are mentioned frequently in texts, especially during the 1920s and 30s, as a presumed 'healthy' treat for children.
'Yorkshire Evening Post' - Friday 17 December 1937