1 large bunch celery with leaves (about 2 pounds)
2 tablespoons olive oil
1 large onion (about 12 ounces), chopped
1 tablespoon fresh thyme leaves
Salt and coarsely ground black pepper
1/2 cup white wine
5 1/4 cups chicken or vegetable broth
2 medium all-purpose potatoes (about 6 ounces each), peeled and cut into 1-inch chunks
2 cups water
Trim ends from celery stalks.
Reserve a few celery leaves for garnish; wrap with plastic wrap and refrigerate.
Slice celery stalks and remaining leaves crosswise into 1-inch pieces; transfer to colander.
Rinse and drain well.
In 5 1/2- to 6-quart saucepot, heat oil over medium heat.
Add celery and leaves, onion, thyme, 1/2 teaspoon salt, and 1/4 teaspoon pepper, and cook 20 to 25 minutes or until celery is soft but not browned, stirring occasionally.
Add wine and cook 2 minutes or until wine is mostly evaporated.
Add broth, potatoes, and water to saucepot; cover and heat to boiling over high heat. Reduce heat to low; cover and simmer 10 minutes or until potatoes are very tender.
In batches, ladle celery mixture into blender; cover, with center part of cover removed to allow steam to escape, and blend very well until pureed.
Pour puree into large bowl.
Repeat with remaining mixture.
Return soup to saucepot; heat through.
Ladle soup into tureen; sprinkle with pepper and garnish with celery leaves.