Salmon & Escarole Packets with Lemon-Tarragon Butter

Preheat oven to 400°F (or see Grill Variation, below).

To prepare packets, start with four 20- to 24-inch-long pieces of parchment paper or foil. Fold in half crosswise. With the parchment or foil folded, draw half a heart shape on one side as you would if you were making a Valentine. Use scissors to cut out the heart shape. Open up the heart.

Combine butter with the juice of 1 lemon in a small pan; melt over low heat. Remove from the heat and stir in tarragon and garlic. Reserve 2 tablespoons for the fish. Combine the rest of the sauce in a large bowl with escarole (or lettuce or spinach), scallions, 1/4 teaspoon salt and 1/4 teaspoon pepper; toss to coat.

Place one-fourth of the greens mixture (about 11/4 cups) on one side of each open heart fairly close to the crease and leaving at least a 1-inch boarder around the edges for folding. Place 1 piece of fish on top of each portion of greens. Season with the remaining 1/2 teaspoon salt and pepper. Brush the reserved sauce on the fish. Slice the remaining lemon and top the fish with the lemon slices.

Close the packet to cover the ingredients. Starting at the top, seal the packet by folding the edges together in a series of small, tight folds. Twist the tip of the packet and tuck it underneath to help keep the packet closed. Place the packets on a large rimmed baking sheet (packets may overlap slightly). Bake until the fish is just cooked through and the greens are wilted, about 15 minutes. (Carefully open one package to check for doneness"be cautious of the steam.) Let the packets rest unopened for 5 minutes before serving.