Spinach-Cheese Squares

Mediterranean Jews so adore fresh spinach that little mountains of the leftover emerald “tails” are a hallmark of their holiday cooking. Called ravikos by Sephardim and testine di spinaci by Italian Jews, these stems are slow-braised until they turn almost red. They are usually served Thursday nights, when it is customary to eat lightly in preparation for the next day’s feasting, and a large stockpile of them has accumulated from the Sabbath preparations.

The leaves of