Step 1

Heat oil in a large heavy pot over medium heat. Add onion, celery, salt and pepper. Cook, stirring occasionally, until the onion is softened and translucent, about 8 minutes.

Step 2

Add broth, carrots, potatoes, apple and bay leaf to the pot. Bring to a boil over medium-high heat; reduce heat to medium-low and simmer until the carrots and potatoes are tender, about 20 minutes. Discard the bay leaf.

Step 3

Working in batches, if necessary, pour the soup into a blender. Secure the lid on the blender, remove the center piece to allow steam to escape and place a clean towel over the opening. Process until smooth, 45 seconds to 1 minute. (Alternatively, puree soup in the pot with an immersion blender until smooth. Use caution when blending hot liquids.) Return the soup to the pot and stir in lemon juice and 1/2 cup half-and-half. Top each serving with celery leaves, if desired, and drizzle each with 1 teaspoon half-and-half.