In a large pot, bring salted water to a rolling boil and cook spaghetti according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

Heat a large skillet over medium-high heat and add butter. Sear diced sirloin or ribeye steak seasoned with Cajun seasoning for about 4-5 minutes until browned.

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

Pour in heavy cream, then add cream cheese, mozzarella, and Parmesan cheese. Stir until melted and smooth, about 3-5 minutes.

Return cooked spaghetti and seared beef to skillet, tossing everything together gently. Add reserved pasta water as needed to loosen the sauce.

Remove from heat, serve in bowls, and garnish with chopped parsley and additional Parmesan or Cajun seasoning if desired.