“The baking of a key inside a bread is a non-Jewish custom which has its foundation in Christian, and possibly even earlier, pagan culture. At least one old Irish source tells how at times when a town was under attack, the men said, ‘let our women-folk be instructed in the art of baking cakes containing keys.
The modern Jewish custom of baking the symbolic shlissel challah, annually takes place on the shabbat immediately following the holiday of Pessah, when tens (if not hundreds) of thousands of religiously observant Jewish women practice this observance.