Preheat your oven to 350°F. To make the meat sauce, cook and crumble 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 turn translucent. Stir in all but ½ cup of the marinara sauce (reserve the remaining ½ cup for later) and combine well. Set this mixture aside. For the noodles, cook the spaghetti according to the package directions until just al dente. Drain and transfer the hot pasta to a large mixing bowl; toss it with the butter and the reserved ½ cup of marinara sauce until well combined. Next, prepare the cheese layer by mixing together the softened cream cheese, sour cream, and cottage cheese until smooth. To assemble the casserole, pour half of the pasta mixture into a 9×13-inch baking dish, then evenly spread the cheese mixture over the pasta. Layer the remaining noodles on top, followed by the meat sauce, spreading it out evenly. Finish by sprinkling the shredded mozzarella and grated Parmesan cheese over the top. Bake for 30 to 40 minutes, or until the casserole is hot and bubbly. Around 20 minutes in, check the cheese; if it’s browning too fast, cover the dish loosely with foil. After baking, let the casserole rest for at least 15 minutes before slicing and serving to allow it to set. Enjoy!