Remove the casserole from the refrigerator 30 minutes before baking.
Pour this mixture over the top of the casserole, cover with plastic wrap, and refrigerate over night.
The casserole will have puffed up and browned around the edges.
1706, "stew pan," from French casserole "sauce pan" (16c.), diminutive of Middle French casse "pan" (14c.), from Provençal cassa "melting pan," from Medieval Latin cattia "pan, vessel," possibly from Greek kyathion, diminutive of kyathos "cup for the wine bowl." Originally the pan, since c.1930 also of the dishes cooked in it, via cookery phrases such as en casserole, à la casserole.