Ina Garten's Creamy Tomato Bisque

Heat butter and oil in a large pot or Dutch oven over medium-low heat. Add onion, shallots, and leek. Cook, stirring occasionally, until tender, 8 to 10 minutes. Add tomatoes, milk, cream, saffron, and red pepper flakes. Bring to a boil over high heat. Reduce heat and simmer, uncovered and stirring occasionally, until flavors are blended and soup is slightly thickened, 30 to 40 minutes. Season with salt and pepper. Serve hot, garnished with Parmesan and parsley.