Bring a large pot of salted water to a boil. Add rigatoni pasta and cook according to package instructions until al dente, about 10-12 minutes. Drain and set aside.
In a medium bowl, toss the steak tips with Cajun seasoning until evenly coated.
Heat olive oil in a large skillet over medium-high heat. Add the seasoned steak tips and cook for 3-4 minutes per side, or until browned and cooked to desired doneness. Remove steak tips from skillet and set aside, keeping warm.
In the same skillet, reduce heat to medium and add butter. Once melted, add minced garlic and sauté for 1 minute until fragrant.
Sprinkle flour over the butter and garlic mixture and whisk continuously for 1-2 minutes to form a roux.
Gradually whisk in whole milk and heavy cream, continuing to whisk until the sauce thickens, about 4-5 minutes.
Stir in grated Parmesan cheese, salt, black pepper, and smoked paprika. Continue stirring until the cheese is melted and the sauce is smooth.
Add the cooked rigatoni pasta to the sauce and toss to coat evenly.
Return the cooked steak tips to the skillet and gently mix them into the cheesy rigatoni sauce.
Sprinkle chopped fresh parsley over the top and serve immediately.