Ice Cream
I remember a segment on Bullwinkle set in Medieval times, and at the end the narrator said that everyone lived happily ever after, because the next year ice cream was invented.
If it was a segment of Peabody's improbable history it might have been the one with King Arthur, or Marco Polo, or Richard the Lionheart, or Robin Hood, or William Tell, or Johannes Guttenburg, or Leif Ericsson.
Or possibly it was one of the Fractured Fairy Tales. It might have been about Dick Whittington, so the 12th episode of the 1st season of Fracture Fairy tales, about Dick Whittington, might be the one I am remembering.