Creating Million Dollar Spaghetti is a straightforward process if you follow these simple steps:

1. Preheat the oven to 350°F (175°C).
2. Cook the spaghetti according to package directions until al dente. Drain and set aside.
3. In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until softened, about 5 minutes.
4. Stir in the garlic and ground beef (or turkey). Cook until the meat is browned, making sure to break it into smaller pieces.
5. Once the meat is cooked through, add the marinara sauce to the skillet. Mix well and let it simmer for a few minutes.
6. In a separate bowl, combine the ricotta cheese, sour cream, Italian seasoning, salt, and pepper.
7. Prepare a baking dish by spreading a thin layer of the meat sauce at the bottom.
8. Layer half of the cooked spaghetti over the sauce.
9. Spread half of the ricotta mixture on top of the spaghetti.
10. Add a layer of half of the remaining meat sauce over the ricotta.
11. Sprinkle half of both mozzarella and cheddar cheeses over the meat sauce.
12. Repeat the layers with the remaining spaghetti, ricotta mixture, meat sauce, mozzarella, and cheddar.
13. Cover the baking dish with aluminum foil and place it in the preheated oven.
14. Bake for 25 minutes. Then, remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden.
15. Once finished, remove the dish from the oven and let it cool slightly.
16. Garnish with chopped parsley before serving.

This step-by-step guide ensures that you create an incredible dish that everyone will rave about.