1. In a blender or food processor, puree tomatoes with their juices until smooth. In a large pot, heat oil over medium. Add onion and garlic and cook, stirring, until onion is soft, about 8 minutes. Add tomatoes and anchovies and bring to a boil. Reduce heat and simmer until slightly thickened, about 15 minutes. Stir in basil and season with salt and pepper. Add spaghetti, toss to combine, and serve sprinkled with Parmesan.