After you've finally finished putting away your Pesach dishes it's time to make Schlissel or Key Challah. It is an old and established custom that on the first Shabbos after Pesach we shape a challah into the form of a key or stick a real key inside a regular challah because this was the Shabbos when the Manna, the miraculous food Hashem air-mailed to our forefathers throughout their desert wanderings, ceased to fall.
Imagine what that Shabbos must have been like. All of the Children of Israel simultaneously wondering whether Manna had gotten lost or misplaced or delivered to the wrong address. But don't feel too sorry for them. Our anscestors had Joshua, Yehoshua Bin Nun to guide them . Remember that he was Moshe Rabeinu's own hand picked successor and protege and like Moshe he had a hotline to Hashem. It was time for the Jewish people to start fending for themselves and eating from the land.
This change indicated that the Children of Israel, we weren't yet called Jews, had entered a new reality. The key symbolizes this. It is a Jewish mystical teaching that Hashem's goodies are locked up and our prayers are the "key's" to opening His storehouse. The act of making Schlissel Challah is in and of itself regarded as a way to draw down the Heavenly blessing of Parnossa or sustenance.
You can either impress a key into a challah dough--be sure to sterilize the key first if you chose that method or do as I did which is to form the challah into the shape of a key. The Sefer Ta'amei Haminhagim (the most leading work on the subject of Jewish customs) recommends the key sculpture (my method) . Unlike a hamentaschen, there isn't a designated shape, just copy the simplest key you've got. You can form one long rope of challah--not too thin and attach another smaller rope on top. Think simple, the kind of key a six year old might fashion from play-doh. This isn't about creating a museum piece.
Here's my machatesteh's (Yiddish for my son in law's mother) recipe for wonderful challot - Key Challah Recipe.