A Florentine is a sauce to make your own. Me I use a Mornay for a base, and aside from the essential spinach, mild peppers or whatever good onion that’s on hand. The sauce should be creamy and savory rather than pungent, and always served hot. A Florentine is best on seafoods; oysters Rockefeller is nothing more than a variation of this standard, and this cream version works well with most light fish and shellfish. Use a hard cheese and do not add parsley, which compromises the spinach. Oil and line a small gratin with peeled shrimp, whole or chopped, cover with Florentine, a dusting of cheese and bake until bubbling in a very hot oven. Crusty bread and plenty of lite Pilsner are always in order.