Pat the steak cubes completely dry with paper towels. In a medium bowl, toss the steak with the Cajun seasoning until evenly coated.

Heat olive oil and butter in a large skillet over medium-high heat until the butter is foaming. Add the steak in a single layer, ensuring not to overcrowd the pan (work in batches if needed). Sear for 1-2 minutes per side until a deep, dark crust forms and the center is pink. Remove steak to a plate and set aside.

Meanwhile, bring a large pot of heavily salted water to a boil. Cook rigatoni according to package instructions for al dente. Before draining, reserve 1 cup (240ml) of the starchy pasta water.

In the same skillet used for the steak, reduce heat to medium. Add the minced garlic and cook for 30-60 seconds until fragrant. Pour in the heavy cream, bring to a simmer, and cook for 2-3 minutes until it thickens slightly.

Remove the skillet from the heat. Gradually add the freshly grated Parmesan cheese, whisking constantly until the sauce is smooth and creamy. Season with salt and pepper to taste.

Add the drained pasta to the skillet with the sauce, tossing to combine. Add a splash of reserved pasta water if the sauce is too thick. Return the steak bites and any accumulated juices to the pan. Stir to combine, garnish with fresh parsley and coarse black pepper, and serve immediately.