There is an interesting tradition still followed in some Ashkenaz Jewish communities of baking challa in the shape of a key for the first Sabbath after Passover. The challa may be shaped as a key, the dough be impressed by actual keys or it may contain a real key inside. It is called shlisl challa, from the Yiddish word for key. The tradition is still followed in Lithuania, Poland and Germany.
According to one version, shlisl challa is connected with a Passover prayer. The key recalls the door to Heaven or Paradise. It is said the upper gates of Heaven open during Passover, and after they close again. To open them, Jews place a key inside the challa loaf. Other Jews object to the entire practice as misguided, superstitious or even idolatrous.
The photos below show challa baked at the Bagel Shop Café for the first Friday following Passover.