Bring one cup lightly salted water to boil in a small saucepan. Add the carrots and simmer until very tender, about eight minutes. Drain, reserving half a cup cooking water in a small bowl.

Stir the matzo meal into the reserved cooking water; let stand 10 minutes to soften and absorb liquid. Put the carrots in a food processor.

Warm the oil in a heavy medium skillet over medium-low heat. Add the onion, salt and pepper lightly, and sauté until soft and shiny, about eight minutes.

Add the scallions and stir one minute. Transfer the onion mixture to the food processor. Add the matzo meal mixture and puree until everything is smooth.

Using an electric mixer, beat three of the eggs and the lemon juice in a large bowl until foamy and slightly thickened, about four minutes. Stir in the mixture from the food processor, but don’t clean the processor yet.

Put the fish fillets, smoked fish, about one teaspoon salt (or to taste), and about 1/4 teaspoon pepper in the food processor. Using on-off turns, chop until fine.

Add the remaining egg and pulse to a coarse paste. Transfer the fish mixture to the bowl and combine thoroughly. Cover and refrigerate until very cold, at least two hours.

Line a large baking sheet with waxed paper. Wetting your hands with cold water if necessary, form the mixture into ovals, using about 1/4 cup for each. Place on the prepared baking sheet. Cover with waxed paper and chill while preparing the cabbage and steamer.

In a large, wide pot with a tight-fitting lid, place a rack that stands about two inches high (if you don’t have a vegetable steamer, a round cake rack works well; if the rack is not high enough, set it over two custard cups or empty tuna cans). Fill the pot with enough water to meet, but not cover, the bottom of the rack.

Line the rack with a layer of cabbage leaves. Arrange eight fish ovals in a single layer on the cabbage leaves; cover the fish with another layer of leaves.

Bring the water in the pot to a boil. Cover the pot and steam the fish over medium heat until cooked through at center and firm to the touch, about 25 minutes.

Transfer top layer of cabbage leaves to a platter. Top with the cooked fish ovals. Cover them with the bottom cabbage leaves. Steam the remaining fish ovals in additional cabbage leaves in two more batches, adding more water to the pot if needed.

Let the cooked gefilte fish cool to room temperature. Keeping the fish covered with the cooked cabbage leaves so it will remain moist, wrap the whole platter with plastic wrap, and refrigerate until cold, at least six hours.

Put the garlic through a press or mince it fine and place in a small bowl.

Stir in the horseradish and lemon juice. Whisk in the mayonnaise.

Season to taste with salt and pepper.

Cover and set aside, refrigerated, at least 30 minutes before serving.

For best flavor, serve the fish chilled but not icy cold.

Remove the fish from the cabbage leaves and arrange attractively on platters or individual plates lined with lettuce, endive, or radicchio.

Accompany with lemon-horseradish sauce.