- Heat oil in a large saucepan or medium soup pot over medium heat.
- Stir in onion and chopped celery; cook until the onion is softened and translucent, 8 to 12 minutes; do not brown.
- Stir in curry powder, and then add carrots (peeled and thinly sliced), apples (peeled and coarsely chopped) and bay leaf.
- Stir well over medium heat for 2 minutes, add broth and salt.
- Bring the mixture to a low boil, and then reduce the heat to low.
- Cover tightly and simmer until the carrots and apples are tender, 20 to 25 minutes.
- Remove the bay leaf. Using a large slotted spoon, transfer the soup solids to a food processor, adding about 1/2 cup of the broth; process to a smooth puree.
- Pour the puree back into the soup. Reheat and season with pepper to taste.
- Serve piping hot, garnishing each serving, if you like, with a dab of yogurt and a sprinkle of fresh herbs.