By: MARTHA ROSE SHULMAN

Time: About 30 minutes, and chilling time (up to a few hours)
Yield: Serves 4 to 6
Advance preparation: You can poach the fish several hours ahead and keep in the refrigerator. The sauce will hold for a day or two in the refrigerator.

Nutritional information per serving: (4 servings, using 1 1/2 pounds fish): 226 calories; 13 grams fat; 2 grams saturated fat; 3 grams polyunsaturated fat; 8 grams monounsaturated fat; 66 milligrams cholesterol; 8 grams carbohydrates; 2 grams dietary fiber; 436 milligrams sodium (does not include salt to taste); 20 grams protein

Ingredients:

1 1/2 pounds ripe tomatoes
1 to 2 garlic cloves (to taste), peeled, green shoots removed
Salt and freshly ground pepper to taste
2 teaspoons balsamic vinegar
3 tablespoons extra-virgin olive oil
1 tablespoon chopped fresh tarragon
1 tablespoon chopped fresh basil (more to taste)
Thin strips zest from 1/2 orange

For the fish:

1 1/2 to 2 pounds petrale sole fillets
Salt and freshly ground pepper to taste
2 basil sprigs
Thin strips zest from 1/2 orange

Directions:

Cut tomatoes in half along the equator. Place a strainer over a bowl and squeeze out seedpods. Rub seedpods against strainer to extract juicy pulp. Discard seeds. Place a box grater in a wide bowl, and using the large holes of the grater, grate tomatoes by rubbing the cut side against the grater, with the skin side cupped in your hand. When you feel the holes of the grater against the inside of the tomato skin, you are done. Add juice from seedpods.
Turn on a food processor fitted with a steel blade and drop in the garlic. When it is chopped and adhering to the sides of the bowl, stop the machine and scrape down the sides with a spatula. Add tomatoes, salt, pepper and balsamic vinegar. Process in machine for 1-2 minutes, until sauce is frothy. With machine running, slowly add olive oil. Alternatively, purée at high speed in a blender for 1 minute, until frothy. Transfer to a bowl, taste and adjust seasonings. Stir in tarragon. Taste and adjust salt and pepper. Cover and set aside at room temperature if serving in an hour or two, or refrigerate for up to a day.
Steam the fish. Prepare the fillets by slapping them – not too hard – with the flat side of a knife, just to break down fibers so they don’t curl too much when you steam them. Season with salt and pepper. You will probably have to steam the fish in batches. Brush your steamer rack with olive oil and place as many fish fillets on top as will fit in one layer. If the fish fillets are too long to lie on the rack, fold them over at the middle. Combine about 1 inch of water and a couple of basil sprigs in the bottom of your steamer and bring to a boil. Place steaming rack in pot and steam fish for 5 minutes, until opaque and fish pulls apart when you insert a fork into it. Remove from heat, transfer to a lightly oiled platter and allow to cool. Sprinkle with orange zest, cover and refrigerate for 30 minutes or longer.
About 30 minutes before you wish to serve, whisk basil and remaining orange zest into the tomato sauce. Taste and adjust seasonings. Remove fish from refrigerator and pour on half the sauce. When ready to serve, spoon some sauce onto each place, top with the fish and more sauce, and serve.