On the first Shabbos after Pesach, many have the custom to eat Shlissel Challah.
The Challah, either braided in the shape of a key or baked with an actual key, is said to be a Segula for Parnassah.
In the video below, you can learn how to make a Shlissel Challah.
https://www.youtube.com/watch?v=gpH1u50zFTY
What is the source in halacha for Shlissel Challa?
This is not an Halacha. It is a Segula.
And what is the source for this Segulah? Where I come from we follow Halachah