Preheat the oven to 325F.

Grease a 12-cup bundt pan with pareve margarine.

Cut the halibut and salmon into large chunks.

Place the fish in a food processor and pulse until finely ground, but not pureed.

Transfer the fish mixture to an electric mixer bowl.

Heat vegetable oil in a large frying pan and sauté diced Spanish onions over medium-low heat until soft and transparent.

Let the sautéed onions cool.

Add the cooled onions, eggs, cold water, matzoh meal, salt, white pepper, sugar, and lemon juice to the fish mixture.

Beat in the electric mixer at medium speed with a paddle attachment for about 10 minutes.

Add the snipped dill and grated carrots; mix well.

Pour the mixture into the greased bundt pan.

Smooth the top with a spatula and cover with foil.

Place the bundt pan in a large pan filled with almost boiling water (bain marie). The water should come at least halfway up the sides of the bundt pan.

Bake in the oven for 1 hour, or until the center is solid.

Cool for 5 minutes, or until the mold is cool to the touch.

Run a knife around the edges to loosen.

Place a flat serving plate on top of the bundt pan and invert the mold onto the plate.

If the mold does not release easily, gently shake the plate.

Refrigerate for several hours or overnight to chill completely.

Slice as you would a torte.

Garnish with parsley and remaining dill.

Serve with prepared red horseradish.