Place the butter in a large saucepan under low heat. Add the white scallion bulbs, red bell pepper and celery. Saute and stir until the vegetables are softened. Add the diced potatoes, 2 cups corn ,bay leaf, broth and salt. Bring to a boil, reduce the heat and simmer stirring occasionally for about 15 minutes.
Puree the remaining 2 cups of corn with the milk in a food processor. Add the milk/corn mixture and the pepper to the soup. Simmer until the soup thickens, about 10 minutes. Remove the bay leaf and stir in the scallion greens. Serve immediately, store any leftover soup in the refrigerator, covered.