For the soup:
3 cups whole milk
3 ears of fresh corn, kernels cut from cobs, cobs broken in half and reserved *
2 tablespoons canola oil
1 large onion, chopped
1 large carrot, peeled, thinly sliced
1 celery stalk, thinly sliced
1 garlic clove, crushed
2 cups water
2 tablespoons parsley, checked and chopped
2 teaspoons dried oregano
1 bay leaf
Ground white pepper
For the garnish:
1/3 cup fresh corn kernels cut from about 1/2 ear of corn
1 scallion, thinly sliced
Pinch of cayenne pepper
Bring milk and reserved corncob halves (not kernels) just to boil in heavy medium pot. Remove from heat, cover, and let steep while sautéing vegetables.
Heat oil in a large saucepan over medium heat. Add onion; sprinkle with salt and sauté until translucent, about 5 minutes (do not let onion brown). Add corn kernels, carrot, celery, and garlic; cook until vegetables are soft, stirring frequently, about 10 minutes. Add 2 cups water, herbs, bay leaf, and milk with corncobs. Increase heat and bring to boil. Cover partially, reduce heat to low, and simmer 20 minutes to blend flavors.
Discard corncobs and bay leaf. Cool soup slightly. Puree soup using a blender until very smooth. Strain into a large bowl, pressing on solids to extract as much liquid as possible. Season soup to taste with salt and white pepper. Cover and chill overnight.
Mix corn, scallions, and pinch of cayenne. This can be made 2 hours ahead. Let stand at room temperature or refrigerate overnight.
To serve, warm soup over medium heat. Divide among bowls. Sprinkle with corn and scallion mixture. Top with a teaspoon of sour cream and serve.
*This recipe can be prepared from frozen corn cobs; just defrost before beginning.