Polish chilled fish in horseradish sauce

Place carrots, celery, parsley, onion, peppercorns, bay leaf, and water in a large pot. Bring to a boil and simmer for 20 minutes. Strain broth and add fish fillets to hot vegetable broth, cooking for 6–10 minutes until the fish flakes easily. Remove fish from broth and arrange fillets on serving platter. Cover and chill. Strain and chill 3/4 cup of the remaining fish broth, reserving it for the sauce. In a saucepan, melt the margarine. Blend in flour until it forms a smooth paste. Add the cooled fish broth gradually, stirring constantly. Cook and stir until the sauce boils. Remove from heat and stir in horseradish sauce, sugar, dash of salt, sour cream, and chopped hardboiled eggs. Cool for 15 minutes. Pour the horseradish sauce over the chilled fish, garnish with shredded lettuce, and serve immediately.