1. Preheat oven to 325°F, and line a large baking pan with oiled foil.
2. Cook the carrots, celery, and onion in olive oil or butter until they start to soften.
3. Place fish stock in a large saucepan. Add all vegetables and and simmer until vegetables are soft.
4. Add fish and continue to cook until fish is white.
5. Add thickener to thicken to chowder consistency.
6. Remove from heat and add heavy cream and seasonings. Serve immediately.