Begin by cutting the sirloin steak into 1 to 1.5-inch cubes. Pat the steak dry with paper towels to help it sear properly, then generously season with Cajun seasoning, salt, and black pepper. Set the seasoned steak aside to allow the flavors to meld while you prepare the pasta and sauce.

In a large pot, bring salted water to a vigorous boil over high heat. Once boiling, add the rigatoni and cook according to package instructions until al dente, usually around 8-10 minutes. Remember to reserve ½ cup of the starchy pasta water before draining the rigatoni, as this will help to thicken your sauce later.

While the rigatoni cooks, heat a large skillet over medium-high heat and add 1 tablespoon of unsalted butter. Once the butter has melted and starts to bubble, add the seasoned steak tips in a single layer. Sear for about 1-2 minutes on each side until beautifully browned. Remove the steak from the pan and tent with foil to keep warm.

In the same skillet where you seared the steak, reduce the heat to medium and add the remaining 2 tablespoons of butter. Once melted, add the minced garlic and sauté for about 30 seconds, stirring continuously until fragrant and golden.

Pour in the heavy cream, stirring well to combine and scraping up any browned bits left in the skillet. Allow the mixture to simmer for 2-3 minutes, letting it thicken slightly, and deepen in flavor.

Stir in the freshly grated Parmesan cheese gradually, allowing it to melt into the sauce while mixing thoroughly. If the sauce appears too thick, adjust the consistency by adding a little of the reserved pasta water.

Once the rigatoni is drained, add it directly to the skillet with the creamy sauce. Toss the pasta gently to ensure it's evenly coated with the luscious mixture.

To plate your delicious Rigatoni in Garlic Butter Parmesan Cream Sauce with Cajun Steak Tips, divide the coated pasta among serving plates. Top each portion with the seared steak tips and sprinkle with fresh chopped parsley if desired.