Question:
What is the “makor” for shlissel challos?
Answer:
The first place where the custom (of baking challot in the form of a key on the first Shabbat after Pesach) is mentioned is in the Ohev Yisrael, Parashat Shemini (likkutim), where he quite lauds the custom.
Several rationales are given, ex post factum of course, for why those who do it should find sense in the idea.
Only serious research will unearth how the custom began.
