Preheat oven to 400 degrees F. Rinse fish well under cold water, dry with paper towels, rub with salt and pepper inside and out. Over moderate heat melt butter in a heavy skillet; when butter foam subsides, add shallots or onions, garlic, and celery. Reduce heat and sauté about 5 minutes, or until vegetables are wilted. Stir occasionally. Add a little more butter if indicated. Turn heat to high, add mushrooms and cook 3 or 4 minutes more. Add chervil, sage, savory, basil, parsley, and 1/2 cup of the wine; stir well, reduce heat, and let simmer for several minutes.

Remove skillet from heat, stir in bread crumbs and grated cheese, lifting lightly with a fork to combine all ingredients. Additional salt and pepper may be added, if required. Allow mixture to cool slightly.

Place one fillet on shallow baking pan lined with greased foil. If fish slabs are thick and it looks as though the dish would be unwieldy when assembled, lay two pieces of twine on pan first and use to tie stuffed fillets together. Use larger piece of fish for bottom, if they differ. Arrange stuffing neatly on top of fish, then lay second fillet on that.

Press stuffing inward if needed to help hold it in place. Rub top of fish with olive oil and dust lightly with salt and pepper if desired. Optional salt-pork slices should be added at this point. Tie with twine if needed.

In a small saucepan heat remaining wine and olive oil and the lemon juice. Pour it over fish and bake, uncovered, about 30 to 45 minutes, or until fish flakes easily when pierced with a fork. While the fish is baking, baste it three or four times with the liquids in the baking pan. Transfer fish to a heated platter and discard twine.

Serve the fish very hot, garnished with lemon wedges and sprigs of parsley.Makes 6 to 8 portions.