Seder

Elijah's Newfangled Cup Eliezer Brodt, Seforim. Opening the door to Elijah and inviting him to drink a cup of wine is a widespread Seder custom today.  But there is no record of this custom anywhere before the 17th century.

The Jew and the Giant Olive Natan Slifkin, Rationalist Judaism. The midrash says a person should eat an olive's worth of matzah at the Seder.  But halakhists today reckon the amount required at 10 times the size of an actual olive.

Deconstructing Dayeinu Avi Shafran, Cross-Currents. "Would it really have 'been enough for us' had God not, say, split the Red Sea, trapping our ancestors between the water and the Egyptian army?"

Plato and the Haggadah Nathan Lopes Cardozo, Cardozo Academy. In the Phaedrus, Plato bemoans the inadequacy of the written word.  So too, on Seder night, it is not sufficient for us to read the Haggadah—we must hear it.

Softening the Bread of Affliction Shayna Zamkanei, Times of Israel. Today, we are accustomed to square, flat, crisp matzah.  But until the 19th century, Jews ate something that "looked very similar to a pita."