More interesting for larger fish, I think—I have most often prepared salmon, trout and bass in this way. The aluminum casing is not particularly attractive from the point of view of serving but, apart from being easy to arrange, it has the advantage over parchment paper of permitting the enclosure of a certain amount of liquid with the fish. The fish may be marinated as for a grilled fish and enclosed in the papillote with its marinade; it may be simply enclosed with a scattering of chopped shallots and 2 or 3 tablespoonsful of white wine, plus a handful of shredded sorrel; it may be placed on a scattering of mirepoix or duxelles, with more of the same spread atop and a bit of white wine added—and so forth. Allow a generous amount of foil—about 4 inches at each end of the fish. Place the foil on the baking sheet before garnishing it: Put the dry materials and the seasoned fish in place, slices of butter atop, and pull the borders of the foil up gently, boat-like, around the fish before pouring in the bit of wine. Fold the edges together, doubly or triply, pinching tightly, beginning at the summit and working first to one end and then to the other—it must be airtight and plenty of space should be left inside the sealed papillote. Bake in a 400° to 450° oven, using the 10-minutes-per-inch time measure. Transfer the package to a heated serving platter, slitting it open at table. The juices are sauce enough.
