I believe that if you're on a diet, you can have your sauce and eat it, too, while also actually enjoying what you eat. Sure, you should watch what foods you eat, and how much of them. But it's also important to make sure that what you eat actually satisfies you. If your food is beautiful, aromatic, and full of flavor, it will take less of it to satisfy your appetite. The fact that your food is also smartly cooked to be lower in calories is a bonus.

All these strategies come together in one of my favorite dishes, a classic I've been making and serving to my customers for more than 25 years: Fish Fillets with Celery Root Cream Sauce.

The recipe features mild-tasting, firm-fleshed fish fillets. As anyone health-conscious will tell you, the more fish you eat, the better for your health and weight. Choose any variety you like in the market that is absolutely fresh and reasonably priced; some of my favorites are sole, turbot, pike, bass and grouper. Be sure to ask your fishmonger to save the bones from the fillets to enhance the cooking liquid.

To complement the delicate fish, I always like a rich-tasting sauce. But "rich" doesn't necessarily mean packed with fat or calories. For many years now, I've made virtually fat-free "cream" sauces by starting with a root vegetable puree and then adding a touch of creamy flavor with a little reconstituted nonfat dry milk.

FISH FILLETS WITH CELERY ROOT "CREAM" SAUCE
Serves 6

2 medium carrots, rinsed
1 medium turnip, rinsed
1 pound asparagus, rinsed
1 pound mushrooms, wiped clean with a damp cloth
Salt
1 lemon
4 small celery roots (celeriac)
4 to 6 tablespoons nonfat dry milk, dissolved in 1/4 cup water
2 cups Chardonnay or white Burgundy wine
2 cups water
2 pounds fresh fish fillets, such as turbot, pike, Dover sole, black bass, striped bass, or grouper, plus bones reserved by fishmonger from filleting
1/4 teaspoon whole black peppercorns
4 sprigs parsley
1 bay leaf
Pinch of dried herbes de Provence
Safflower oil or other flavorless vegetable oil
Chopped fresh parsley or shredded fresh basil leaves, for garnish

In this particular recipe, the root vegetable on which I base the sauce is celeriac, the knobby-looking root of a plant related to the one that yields crispy stalks of celery. Celeriac, also called celery root, contributes a delicate, refreshing flavor and pale ivory color to the sauce. If you like, feel free to substitute parsnips or carrots, or a blend of two or even three vegetables, for a different tint and taste.

Poaching in water flavored with the fish bones, the peels of vegetables that garnish the dish, and a selection of fresh and dried herbs gives the fish a subtle yet complex flavor, without any added fat calories. The final presentation of fillets, colorful vegetables, and smooth "cream" sauce create a beautiful dish that proves one of my favorite lessons about cooking: We eat with our eyes before food ever touches our lips.

With a swivel-bladed vegetable peeler, peel the carrots, turnip, and asparagus, placing the peelings in the bottom half of a steamer. With a small, sharp knife, cut the carrots, turnip, asparagus, and mushrooms into 1-by-1/4-inch pieces. Bring a saucepan of salted water to a boil and add a squeeze of lemon juice. One at a time, cook each vegetable in the water until tender but still crisp, 1 to 2 minutes at most, removing each batch with a slotted spoon or wire skimmer and transferring to a bowl. Cover and keep warm.

Carefully peel the celery roots and cut them into quarters. In lightly salted boiling water, simmer them until very tender, 10 to 15 minutes. Drain well. Put the celery roots in a blender or food processor and process with enough of the reconstituted milk to make a thick, very smooth puree. Press the puree through a fine-meshed sieve to remove any fibers. Set aside and keep warm.

To the vegetable peels in the bottom half of the steamer, add the wine, water, fish bones, peppercorns, parsley, bay leaf and herbes de Provence. Bring to a boil over high heat.

Meanwhile, cut the fish fillets into thick, finger-sized strips, about 1 by 3 inches each. Brush the steamer rack with oil and arrange the fish pieces in a single layer. Cover and steam until just cooked through, opaque and barely flaky, 5 to 7 minutes. Remove from the steamer, cover, and keep warm.

Strain the liquid from the bottom of the steamer into a saucepan. Boil over high heat until the liquid reduces to 1 cup, about 15 minutes. Stir in the celery root puree. Taste the sauce and correct the seasonings with salt, pepper, and lemon juice.

To serve, arrange the fish strips in individual shallow serving bowls or plates. Arrange the cooked vegetables on top and spoon the sauce around the fish and vegetables. Garnish with parsley or basil and serve immediately, passing extra sauce on the side.