Florentine recipes will typically feature some main ingredient, such as meat, poultry or fish, served on a bed of spinach, and then topped with a Mornay sauce. A Florentine recipe may also be topped with cheese which is browned or au gratin.
One common Florentine recipe is Eggs Florentine, which is a variation on Eggs Benedict. Eggs Florentine features a poached egg over a bed of spinach on a grilled English muffin, and topped with Mornay sauce (although it's common to serve it with Hollandaise sauce instead).
Note that the word florentine also has another definition not related to recipes made with spinach and Mornay sauce. There's a thin, crunchy wafer or cookie that also goes by the name florentine. This florentine cookie is made with honey and nuts and is sometimes coated with chocolate.