The next time you get the gift of an extra doughnut added to your dozen, thank crooked 13th-century bakers for the bonus treat. In the 1260s, British breadmakers were notorious for shorting customers with skimpy loaves.
King Henry III was so irked by the problem that he implemented a new law to standardize the weight of a loaf—selling puny loaves could result in beatings or jail time.
Since bakers wanted to stay on the right side of the law, one common trick was to give 13 loaves to any customer buying a dozen. Even if the loaves were light, the extra would cover the shortfall. It was an easy fix for bakers, and since low-carb diets were still seven centuries away, customers rejoiced.