Cook spaghetti noodles in a large pot of salted water, according to package instructions, until al dente. Do not overcook. Drain and set aside.
16 ounces spaghetti noodles
Preheat oven to 350F.
Meanwhile, in a large skillet, combine Italian sausage, ground pork, ground beef, and onion. Cook until meats are no longer pink and onion is tender; drain off any excess oil.
1 pound mild Italian sausage, 1 pound ground pork, 1 pound ground beef, 1 cup onion chopped
Add marinara sauce to the skillet and stir to combine; set aside.
48 ounces marinara sauce
In a medium bowl, beat together ricotta, cream cheese, sour cream, egg, and italian seasoning.
15 ounces ricotta cheese, 1 large egg, 8 ounces cream cheese softened, 1/4 cup sour cream, 3 teaspoons italian seasoning
Spoon 1 cup of the meat sauce into the bottom of a 9×13 baking dish.
3 cups grated mozzarella cheese, 1 cup grated parmesan cheese, 1/2 cup butter
Add half of the butter.
Layer half of the spaghetti noodles.
Layer half of the meat mixture.
Layer half of the ricotta mixture.
Layer half of the mozzarella and parmesan cheeses.
Repeat layering for the remaining half of the ingredients. The ingriedents look like they will not fit in the baking dish, but they will.
Bake for 60 minutes until cheese is fully melted and the sauce is bubbling up around the sides of the dish. If desired, broil for 2-3 minutes to brown the top of the cheese.