Bring a large pot of salted water to a rolling boil to prepare for cooking the rigatoni pasta.

Pat the steak cubes dry with paper towels, then toss them with 1 tablespoon of Cajun seasoning, and season with salt and pepper. Heat olive oil and 1 tablespoon butter in a skillet over medium-high heat. Add the steak cubes and sear until browned on all sides, about 3-4 minutes. Remove the steak from the skillet and set aside.

Add rigatoni to the boiling salted water and cook according to package directions until al dente, usually about 10-12 minutes. Before draining, reserve 1/2 cup of the pasta cooking water; this will help adjust the sauce consistency later. Drain the pasta and set aside.

In the same skillet used for the steak, melt the remaining 1 tablespoon butter over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant. Pour in the heavy whipping cream, stirring and scraping up any browned bits from the pan to incorporate extra flavor.

Gradually stir in the freshly grated Parmesan cheese and shredded mozzarella (if using) until fully melted and the sauce is smooth and creamy. Lower the heat to medium-low to keep it warm without boiling.

Return the seared steak to the skillet and add the cooked rigatoni pasta. Toss everything together gently, adding reserved pasta water as needed to adjust the sauce to a desired creamy consistency. Taste and adjust seasoning with additional Cajun seasoning, salt, and black pepper if needed. Serve immediately while hot and enjoy.