It's an old tradition that's now become mainstream: for the first Shabbat following the holiday of Passover, making challah in the shape of a door key (schlissel in Yiddish). Here's how to create the schlissel shape for your first challah back in the land of the leavened.
The key shape expresses the hope to "unlock" prosperity, the economic flourishing that allows our higher selves and purposes to be actualized. It also has the valence of doors being open to us, having just experienced the redemptive story of Passover. Baking challahs in special shapes for particular Shabbatot or holidays is an old custom, as is the practice of segulot, or rituals to promote positive outcomes. Schlissel challah represents both customs and has become much more widely practiced in recent years. There is a thoughtful article on this on the Book of Doctrines and Opinions, a Jewish thought blog.
There are various ways to form a key shape, and other traditions are baking an actual key into the challah or imprinting it with a physical key. Here we're going with a common version, a skeleton key with a braided shaft and a twisted handle. (Some people make a round twist or make three little challah buns to form the shape of the handle.)
Dividing the dough
You'll want to divide your lump of challah dough (the amount for one loaf) in an unconventional way: first, divide it into three parts (the vertical cuts in the photo at top left), one large, one medium, and one small. Next, you'll further divide the large portion into whatever number of strands you'd like your center braid, the shaft of the key, to be. I decided to make a 4-strand braid, so I divided my large portion into four equal subdivisions, as shown in the photo above left.
After everything's divided, roll each piece into a strand. You should have one short strand, one long strand, and strands of equal length for your braid (again, I'm making a 4-strand braid, so I have four equal, medium-length braids, as in the photo above right).
Make the shaft of the key
For the shaft of the key, we're going to be making a braid, just like a regular challah, but a bit smaller and longer. Any braid will work here, including a regular 3-strand braid; I used a 4-strand braid.
After the center is braided, take the smallest strand of dough and cut it in half. Then, take the cut side and firmly press it into the key on the lower left of the braid, forming the, um, key part of the key, I suppose.
Make the key's handle
Again, there are lots of different ways to fashion the handle part of the key; I made a cloverleaf twist. It's simple to do: form a loop in the center of the remaining long strand of challah dough (photo at top left). Then, take one end of the strand and loop it up, tucking the end under the center (photo at top middle). Finally, take the remaining edge, loop it up, and tuck under at the center (photo at top right). Flatten the top of the key shaft slightly, then press the twist firmly into the top of the braid.
Now, coat with egg wash and bake as you normally would. Your schlissel challah will probably need 5 to 10 minutes less bake time, so check it earlier than you would a regular loaf of challah.