Granny Smith's yearly tradition of baking the family's secret fruit cake recipe, which strangely is immediately followed by the Apple's yearly visit to the doctor and the dentist.
No pony's actually seen Granny bake it, it just seems to appear on a plate every year. Family legend says it's the same fruit cake Great Grandma Sew 'n Sow baked a nearly 100 years ago, it just keeps growing back from the uneaten portion.