In a large saucepan, melt 1 tablespoon of the butter in 1 tablespoon of the olive oil. Add the sliced onion and smashed garlic and cook over moderate heat, stirring occasionally, until softened, about 5 minutes. Add the tomatoes and their juice, the water, heavy cream, sugar, crushed red pepper, celery seed and oregano and season with salt and pepper. Bring the soup to a boil over high heat, breaking up the tomatoes with the back of a spoon. Reduce the heat to moderate and simmer for 10 minutes.