Preheat oven to 200°C and cover a gratin dish with butter. Spice fish fillets with salt, pepper and lemon juice. Dice fillets and put them into gratin dish. Cut ham into stripes and grate carrots. Blend both and sprinkle over fish fillets. Mix well cream,sour cream and spices. Season to taste with salt and pepper and pour over fish-vegatable mixture. Let all simmer coverd in oven for 30 minutes.