1. Boil a large pot of salted water and cook the spaghetti until al dente (8-10 minutes). Drain and reserve 1 cup of pasta water for later use.
2. Heat 1-2 tablespoons of butter and 1 tablespoon of olive oil in a large skillet over medium heat. Add minced garlic and diced red onion, sautéing until aromatic and softened (about 2-3 minutes).
3. Pour in the tomato passata or crushed tomatoes, stirring occasionally. Add dried or fresh basil, and let the sauce simmer for about 5 minutes for the flavors to meld.
4. Reduce the heat to medium-low and stir in heavy cream and cream cheese, allowing them to melt into the sauce. Slowly add mozzarella, Parmesan, and Romano cheeses while stirring until the sauce becomes creamy and smooth.
5. Toss the cooked spaghetti into the skillet with the creamy tomato sauce. Use tongs to coat the pasta evenly. Add reserved pasta water as needed to achieve the desired sauce consistency.
6. Taste and adjust the seasoning with salt and pepper. Sprinkle chili flakes for heat if desired.
7. Garnish the dish with fresh parsley and additional Parmesan cheese before serving for an extra touch of flavor.
8. Serve immediately with a side of green salad or garlic bread for a complete meal.