Bring a large pot of salted water to a rolling boil. Add in spaghetti and cook until al dente, about 8-10 minutes. Drain, reserving a cup of pasta water, and set aside.

Season diced beef with Cajun seasoning. In a skillet, heat butter, add beef, and sear for 3-4 minutes until browned. Remove and set aside.

In the same skillet, reduce heat, add minced garlic, and sauté for about 1 minute until fragrant.

Pour in heavy cream and add cream cheese, mozzarella, and Parmesan. Stir over medium heat until smooth and creamy, about 3-4 minutes.

Add cooked spaghetti and seared beef back into the skillet. Toss until well-coated in the sauce. Add reserved pasta water as needed for consistency.

Remove from heat, garnish with chopped parsley, and serve hot with additional cheese and Cajun seasoning.