Why is the number in a baker’s dozen 13? Nothing to do with what normally is associated with the number 13!
Back in the 13th Century, during the reign of Henry III the Assize of Bread was decreed, the first recorded law decreeing at what weights bread must be sold as. Failure to comply could result in the severe punishment of the baker having their hand chopped off! Ouch!!!
In order to avoid being called a cheat, the baker would slip an extra bun to make sure he was definitely not under supplying his customer.
If you are interested in discovering more about the Assize of Bread, here are some of the sources I have used (please note that this is an affiliate link to Amazon and if you purchase through this link you will be helping Flour-and-Spice): I can highly recommend Elizabeth David’s book: English Bread and Yeast Cookery I have referred to this over and over again for longer than I can remember, it is packed with useful information if you are interested in the history of bread and anything related to baking. Another source is Six Thousand Years of Bread: Its Holy and Unholy History by H.E. Jacob