"Little Jack Horner" in the nursery rhyme may refer to the man who was chief steward to the Abbot of Glastonbury in the early sixteenth century.  If so, then the "plum" he pulled from his Christmas pie was actually:

The Abbot of Glastonbury, seeking favor with the king, sent Jack Horner to the palace with the gift of a pie in which had been placed twelve deeds to manor houses.  When the King received the pie, there were only eleven deeds - the deed to the Manor of Mells was missing.  The Horner family lives in the Manor of Mells to this day, but they have always denied that the rhyme refers to them.