Baking fish fillets en papillote (pronounced pah-pee-ote, meaning "in paper") holds in flavor and moisture. This centuries-old technique usually calls for parchment paper, but while aluminum foil doesn't look as dramatic, it is easier to use. You must rely on blind faith when cooking en papillote because it is not advisable to open the packages to check for doneness. Be sure that your oven temperature is accurate by using an oven thermometer. For a lighter sauce, substitute 1 teaspoon of dark Asian sesame oil for each tablespoon of butter in the foil packages.

CASHEW COD IN FOIL ENVELOPES
Makes 4 servings

1 tablespoon vegetable oil
1 red bell pepper, seeds and ribs discarded and cut into long, ¼-inch-wide strips
4 scallions, white and green parts, chopped
1 tablespoon shredded fresh ginger (use large holes of a box grater)
1 garlic clove, finely chopped
4 ounces sugar snap peas
Salt and freshly ground black pepper to taste
Four 6-ounce cod fillets
4 tablespoons soy sauce, divided
4 tablespoons unsalted butter, divided
½ cup unsalted roasted cashews, very coarsely chopped

Position a rack in the center of the oven and preheat the oven to 400 degrees F. Have ready four 12-inch squares of aluminum foil. Lightly oil the dull sides of the foil squares. Fold each square in half.

Heat the oil in a large skillet over medium-high heat. Add the red pepper and cook, stirring often, just until it begins to soften, about 1 minute. Add the scallions, ginger, and garlic, and stir until the garlic gives off its aroma, about 30 seconds. Remove from the heat, add the sugar snap peas, and stir just until they are coated with the oil. Season the vegetables lightly with salt and pepper.

Lightly season the cod with salt and pepper. Open the foil square and place a fillet on the bottom half. Top with one-fourth of the vegetables, 1 tablespoon soy sauce, and 1 tablespoon butter, cut into a few pieces. Sprinkle with one-fourth of the chopped cashews. Fold the square over to enclose the fish and vegetables, and tightly crimp the edges closed. Place on a large baking sheet. Repeat with the remaining fish, vegetables, soy sauce, and butter.

Bake for 15 minutes. Remove from the oven and let stand for 5 minutes (this will complete the cooking of the fish).

To serve, place a foil packet on each dinner plate. Allow everyone to open each foil package by piercing it with the tip of a sharp knife. You can spill the contents of the package onto each plate or eat directly out of the foil. Take care: the escaping steam can be very hot!