In a large soup pot, heat oil over medium heat. Add onions and celery, cook stirring occasionally, until the onions are soft and translucent (about 5 minutes). Add clam juice, potatoes and thyme. Cook covered over low heat until the potatoes are tender, about 15 minutes. Remove pan from heat.
With a slotted spoon, transfer about 3/4 of the vegetables to a blender and puree. Return puree to soup and bring back to a simmer over medium-low heat. Add vermouth, milk, trout and green onions and heat through. Season with lemon juice, salt and pepper. Ladle into bowls and serve.
From the Dinner Co-op