Bring the clam juice to a boil. Heat a pot with olive oil and butter until the butter melts. Sauté the onions and garlic together, but do not let them brown. Add the celery and red bell pepper, and cook for 2 minutes.

Add the leeks, cover the pot, and let the vegetables sweat. Add the flour, mix well, and cook for about 3 minutes, stirring often. Do not let it stick or burn on the bottom of the pot. Pour in the milk, hot clam juice, bay leaf, and salt, and stir well. Bring to a boil.

Add the corn and potatoes, and bring the soup to a boil again. Let it simmer for about 15 minutes, until the potatoes are cooked. Stir in the clams, black pepper, and fresh herbs. Bring the soup to a rapid boil, then turn off the heat. Serve immediately.