This is a simple, clean-tasting, elegant, old-fashioned dish. The delicate flavors are best appreciated with a simple accompaniment, such as white rice, or alone in a meal of a few courses. For instance, start with Handmade Egg Noodles tossed with butter, herbs, and Sautéed Mushrooms then serve this stuffed sole all by itself; then serve a green salad with sliced oranges and Citrus Vinaigrette. For most occasions, I like this sole unadorned with any sauce besides the pan juices. But on occasions when a sumptuous sauce is appropriate, try using a lemon butter sauce.
Adapted from "The Commonsense Kitchen" by Tom Hudgens.
Trim the sole so the pieces are roughly of even size, reserving the trimmings. Chop the trimmings finely with a sharp knife.
Sprinkle the fillets with ¼ teaspoon of the salt, and keep both the fillets and the chopped fish cold in the refrigerator.
Cut out any discolored, shriveled, or browned parts off of the leeks. Cut away all the darker-green top parts, keeping them separate from the white and pale-green bottom portions. Rinse a handful of the longest dark-green leek tops (discard the rest or save for stock), chop coarsely, and arrange over the bottom of an 8-by-8-inch baking pan. (These provide moisture and deepen the leek flavor.)
Trim the dirty root end off the white and pale-green bottom part of the leeks, then halve lengthwise. Under cool running water, rinse the leeks, making sure all the outer layers get thoroughly rinsed — they easily trap sand and dirt. Drain, then cut the leeks into small dice.
Heat the oven to 350 degrees. Melt a tablespoon of the butter in a small saucepan over medium heat. Add the diced leeks with ½ teaspoon salt and stew, stirring frequently but otherwise keeping the pan covered, until tender, 7-10 minutes. If the leeks seem dry, add teaspoonfuls of water as necessary — the leeks shouldn’t brown. Remove from the heat. You should have about 1 cup of tender, cooked leeks.
Remove the sole fillets from the refrigerator. Have toothpicks on hand. Stir the chopped fish into the leeks quickly with another ¼ teaspoon salt. Spread the leek-fish mixture evenly over the fillets, roll the fillets up, starting with the thicker end, and secure each roll with a toothpick. Place the rolls toothpick side down on the bed of leek tops in the baking pan. Put a thin slice of butter atop each roll. Bake for about 20 minutes, or until the fish is cooked through.
Using a wide spatula, carefully transfer 2 rolls to each person’s plate, then slide out the toothpicks. Some juice will have accumulated in the baking pan; spoon it over the fish.