Step 1

1 Preheat the oven to 400 degrees with racks in the lower and upper thirds

Step 2

2 Cut four 24-inch-long sheets of parchment paper

Step 3

3 Fold each sheet in half, forming a 12-by-15-inch rectangle and, with a pencil, draw a half-heart shape on the paper, centering the heart on the folded edge and making the heart as large as you can

Step 4

4 Using scissors, cut out the hearts

Step 5

5 (The heart shape makes sealing easier

Step 6

6 )

Step 7

7 Open the heart shapes flat on your counter and lightly butter or oil the center of one side of each

Step 8

8 Place a quarter of the spinach close to the crease on the buttered side of each piece of parchment paper

Step 9

9 Season lightly with salt and pepper

Step 10

10 Divide the fish fillets among the packets, placing them directly on the spinach

Step 11

11 (If the fillets are less than 1-inch thick, fold or tuck them into compact bundles that are about 1 inch thick

Step 12

12 ) Season the fish with salt and pepper and top each with shallots, herbs and tomatoes

Step 13

13 If using butter, cut it into smaller pats and place on top of the fillets

Step 14

14 If using oil, drizzle a little over each fillet

Step 15

15 Splash the wine over the top

Step 16

16 Fold the other half of the paper over to cover the fish

Step 17

17 Then, starting at the top of the heart shape, working with about 2 inches of the edge at a time, fold over about 1/2 inch, pressing down and rubbing your thumb across the fold to make a crisp crease

Step 18

18 Move a little way along the edge and fold over a couple more inches, so that your folds are overlapping and double-folded

Step 19

19 Continue working your way around the edge of the packet, making overlapping folds, like pleats, always pressing firmly and creasing so that the folds hold

Step 20

20 Don’t expect the folded edge to be perfectly even; it will be somewhat crooked — this is part of its charm

Step 21

21 Go back around, making a second fold at any place that doesn’t appear tightly sealed

Step 22

22 If there’s a slight “tail” when you reach the end, give it a twist to seal

Step 23

23 (If you don’t quite master the seal, you can make a quick cheat by stapling or paper-clipping the edges in place

Step 24

24 )

Step 25

25 Arrange the packets on two large rimmed baking sheets so that they don't touch

Step 26

26 Bake for 14 minutes

Step 27

27 (If the fish packets have been in the refrigerator, increase the time to 18 minutes

Step 28

28 )

Step 29

29 Either place the packets directly on dinner plates and provide scissors so that your guests can snip open their own packets at the table, or carefully cut open the packets in the kitchen and slide the contents out onto dinner plates or pasta bowls and serve right away