Answer:
13 of every items because if one of the bakers items are burnt or bake wrong they have one extra
A baker's dozen contains 13 items. It originated as a practice among bakers in 13th century England, when strict laws could have lead to a baker getting his hand chopped off for trying to shortchange a customer.
A Baker's Dozen is 13. The term stems from the baker's tradition of adding one more to a dozen as lagniappe (a 'Cajun word meaning "a little extra").
A normal dozen is 12 (twelve) but bakers bake one extra in case a biscuit , cake , cookie etc. gets burnt or goes wrong , they have a spare.