What does “baking tradition” mean?

Question

She agreed to marry him on one condition: that they have 12 children. True to the old baking tradition, they made 13.

Source

What does the old baking tradition mean? There's no mention of baking in the context.

I can understand this sentence as a whole. But since I'm trying to translate this into another language, I cannot translate it without understanding what the old baking tradition is.

Answer 1

From the Wikipedia entry:

A baker's dozen, devil's dozen, long dozen, or long measure is 13, one more than a standard dozen. The practice of baking 13 items for an intended dozen was insurance against the items being lower than the statutory weight, or of lower than usual quality, which could cause the baker to be fined.