Preheat your oven to 350 degrees F. Prepare the meat sauce by cooking and crumbling the ground beef and Italian sausage in a large skillet, seasoning with salt and pepper. Drain most of the grease, then add the chopped onions and minced garlic, cooking until the onions become translucent. Stir in all but ½ cup of the marinara sauce, reserving that ½ cup for later, and set the mixture aside. Cook the spaghetti noodles according to the package directions until just al dente. Drain and place the hot pasta in a large mixing bowl; add the butter and the reserved ½ cup of marinara sauce, tossing to combine. For the cheese layer, mix together the cream cheese, sour cream, and cottage cheese until well blended. To assemble, spread half of the pasta into a 9×13-inch baking dish, then evenly layer the cheese mixture on top. Add the remaining noodles over the cheese, then pour the meat sauce over everything, smoothing it out evenly. Sprinkle the top with mozzarella and Parmesan cheeses. Bake for 30-40 minutes until hot and bubbly, checking at around 20 minutes to cover with foil if the cheese begins to brown too fast. Allow the casserole to rest for at least 15 minutes before slicing and serving. Enjoy!