1. Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish with melted butter or olive oil and set aside.

2. Bring a large pot of well-salted water to a boil. Add the spaghetti and cook until just shy of al dente, 1–2 minutes less than the package directions. Drain well and toss with 1–2 tablespoons of melted butter or olive oil to prevent sticking.

3. While the pasta cooks, heat the olive oil in a large skillet over medium-high heat. Add the ground beef and Italian sausage, breaking the meat apart with a spoon, and cook until browned and no longer pink. Drain off excess fat if needed.

4. Add the chopped onion to the skillet and cook until softened and lightly golden, about 4–5 minutes. Stir in the minced garlic and cook for 30 seconds, just until fragrant.

5. Mix in the tomato paste, Italian seasoning, salt, black pepper, and crushed red pepper flakes if using. Cook for 1 minute to bloom the flavors.

6. Pour in the marinara sauce, stir to combine, and reduce the heat to low. Simmer the sauce for 5–10 minutes so it thickens slightly and the flavors meld. Taste and adjust seasoning if needed.

7. In a large mixing bowl, combine the softened cream cheese, sour cream, and ricotta cheese. Beat or stir until smooth and creamy. Fold in 1 cup of shredded mozzarella and 1/4 cup grated Parmesan. Season the mixture with a pinch of salt, pepper, and a small pinch of Italian seasoning.

8. Toss the cooked spaghetti with about 2 cups of the meat sauce until the noodles are well coated. Reserve the remaining sauce for layering.

9. Spread a thin layer of the reserved meat sauce over the bottom of the prepared baking dish. Add half of the sauced spaghetti in an even layer.

10. Dollop and gently spread the creamy cheese mixture over the spaghetti layer, going almost to the edges. Top with the remaining spaghetti and a generous layer of the remaining meat sauce.

11. Sprinkle the top evenly with the remaining 2 cups of shredded mozzarella and the remaining 1/4 cup grated Parmesan cheese.

12. Cover the baking dish tightly with foil and bake for 25–30 minutes, until the casserole is hot and bubbling around the edges.

13. Remove the foil and bake for an additional 10–15 minutes, or until the cheese on top is melted, lightly golden, and browned in spots.

14. Remove the casserole from the oven and let it rest for at least 10 minutes before slicing. Garnish with chopped fresh parsley or basil, cut into squares, and serve warm.