Tear off four sheets of aluminum foil, 12 inches wide by 18 inches long. Rub the softened butter in the center half of each sheet.
Peel the grapes and slice them into small coins.
Place a sprig of parsley and a fourth of the celery on one side of the foil sheet. Place two fish fillets, head ends together, on top of the parsley and celery. Spoon the tomato puree lightly over the fish, and top with the grape coins. Sprinkle a little white wine over the fish, and season with salt and pepper.
Fold the foil over. Fold the edges and crimp to make a tightly-sealed envelope. Repeat the process for the remaining fish.
Place the envelopes on a baking sheet and bake in a 400-degree oven for about 12 minutes. The envelopes should puff up somewhat.
Serve the fish in the envelope on the plate. Each guest will open his or her envelope, and the aromas will waft up right into their nostrils.