O. Henry was a master of irony. Almost all of his short stories dealt with the ironies of life. This is also true of the story "Witches Loaves." The title is ironic for two reasons. One is that he alludes to Miss Martha using a recipe of "a mysterious compound of quince seeds and borax," which was supposedly for her complexion. Yet, he leaves the impression that it is also something that a wise woman, or witch, who might be versed in herbal lore, might do to create a love spell.
The second, and more ironic use of the title indicates that the man, Blumberger, calling her an "old cat" when she inadvertently ruins his drawings because her romantic fancy of him as a starving artist prompted her to add butter to his stale bread, considers her the equivalent of a witch who put an evil spell on him and destroyed his work.