1. Place a large pot of cool water over high heat and add in the salt and oil.
2. Meanwhile, to kill two birds with one stone, you can use this time to chop up the spinach. Add it to a medium-sized bowl along with the sour cream, ricotta, Mozzarella, and seasonings, stir well, and set aside.
3. You can also combine the 5 cups of Mozzarella and 4 cups of Cheddar in a big bowl and combine the 1 cup of Mozzarella and Cheddar for the top of the Lasagna in a small bowl.
4. Then, chop up the onions and mushrooms.
5. By this time, the water should have come to a boil. Add the lasagna and let it cook until al dente, about 12 minutes. Once done, remove it and lay it separately on the sides of a colander.
6. Meanwhile, place a skillet over medium heat, add the ground beef and sweet Italian sausage, and chop the meat up as finely as possible with two spatulas until it’s no longer pink.
7. Drain some of the fat but keep most. Add the onions, mushrooms, and seasonings and continue cooking for another 5 minutes.
8. Then add in the sauce, diced tomatoes, tomato paste, and sugar, then stir well and simmer for 5 minutes. 
9. Preheat the oven to 350 degrees.
10. Layer the ingredients in a large lasagna pan (A little meat sauce, lasagna, sour cream mixture, Mozzarella and Cheddar, meat sauce, lasagna, sour cream mixture, Mozzarella and Cheddar, meat sauce, lasagna, meat sauce, and then the 2 cups of Mozzarella and Cheddar for the top).
11. Garnish the lasagna with parsley flakes, and cover with aluminum foil.
12. Bake the Lasagna for 30 minutes covered and 15 minutes uncovered then remove.