Preheat the oven to 350˚F. Bring water to a boil for the pasta. Add the pasta to the boiling water and cook until al dente. Drain and rinse with hot water. Return to the pot, and stir in four tablespoons of butter, and set aside.
While waiting for the water to boil, brown the ground beef with minced onion, seasoned salt, and pepper. Drain off any excess grease off of the browned hamburger, stir in the spaghetti sauce, and set aside.
Next make the alfredo sauce. Bring the heavy cream, minced garlic, pepper and salt to a boil over medium heat. Add the butter, cream cheese, and sour cream. Stir until smooth and heat until it starts to boil. Use a whisk (or a fork), to stir in the shredded Parmesan, one cup at time, until smooth.
To assemble the layers, spread half of the spaghetti noodles in a greased 9×13-inch pan. Pour the alfredo sauce over the noodles. Top with the remaining spaghetti noodles. Spread the spaghetti sauce mixture over the spaghetti noodles. Top with two cups of shredded mozzarella cheese. Bake at 350˚F for 35-45 minutes. If your pan is very full, I would suggest putting a piece of foil or a baking sheet underneath to catch any spills.