In a large saucepan, heat the oil over medium-high heat. Add the onions, celery, and carrots. Season with the salt, cayenne, and black pepper. Sauté for 4 to 5 minutes. Add the garlic and tomatoes. Cook for 3 to 4 minutes, stirring often. Add the broth and bring to a boil. Reduce the heat to medium and simmer, uncovered, for 1 hour and 15 minutes. Remove half of the mixture and puree it in a blender or food processor. Return it to the pot. Add the basil and serve. Or refrigerate and serve chilled.
Makes 8 to 10 servings