Preheat your oven to 350°F (180°C) and coat a 9x13-inch baking dish with cooking spray. Cook the spaghetti in salted boiling water according to the package instructions. Drain the pasta and return it to the pot.
Cooking spray, 1 pound uncooked spaghetti
In a skillet over medium-high heat, brown the ground beef and sausage, breaking it into small pieces. Add the chopped onion and minced garlic, cooking until the onion softens. Stir in the marinara sauce and remove the skillet from heat.
12 ounces ground beef, 12 ounces bulk fresh pork sausage, 1 cup yellow onion, 1 teaspoon finely garlic, 3 cups marinara sauce
Add the butter to the cooked spaghetti and stir until melted. Mix the meat sauce into the pasta, ensuring it is evenly coated.
2 tablespoons unsalted butter
In a separate bowl, combine the cream cheese, ricotta, and Parmesan cheese. Stir until the mixture is smooth and creamy.
8 ounces cream cheese, 1 cup whole milk ricotta cheese, ½ cup parmesan cheese
Spread half of the pasta mixture into the prepared baking dish. Evenly layer the cheese mixture over the pasta, then add the remaining pasta on top. Sprinkle the mozzarella cheese evenly over the casserole.
1 cup mozzarella cheese
Bake in the preheated oven for 30 minutes, or until the cheese is melted, golden, and the sauce is bubbling around the edges. Let the casserole rest for 10 minutes before serving. Garnish with chopped parsley and serve warm.
Chopped fresh flat-leaf parsley