Melt the butter in a large pot over medium heat. Add the onion, celery, and potatoes. Cook and stir until the vegetables are tender, about 10 minutes.
Stir in the flour until evenly blended. Slowly pour in the chicken broth and milk, stirring constantly. Season with thyme, salt, and pepper. Bring the mixture to a boil, reduce heat to low, and simmer for 15 minutes.
Stir in the clams and simmer for an additional 15 minutes. Remove from heat and stir in the parsley. Serve hot.
Interesting Facts
The word "chowder" comes from the French word "chaudiere," which means "cauldron" or "cooking pot."
Maine is the state that is most famous for its clam chowder.
Clam chowder is often served with oyster crackers or fresh-baked bread.