In a large Dutch oven or soup pot, melt butter over medium-high heat. Add onion, celery and garlic; sauté 2–3 minutes, or until tender.
Add broth, potatoes, corn, thyme, salt and pepper. Bring mixture to a boil, reduce heat to medium-low, and cook, stirring occasionally, 10–15 minutes until potatoes are tender.
Stir in chicken; cook 2 minutes until mixture is heated through.
Transfer 3 cups to a large blender. Remove stopper, and cover hole with a folded towel; blend until almost smooth.
Stir into remaining soup mixture. Ladle soup into serving bowls, and garnish with thyme, if desired.
