Season steak tips generously all over with Cajun seasoning, pressing it into the meat. Heat olive oil and 1 tablespoon butter in a 12-inch heavy skillet over medium-high heat until butter stops foaming. Add steak tips in a single layer and sear for 2 to 3 minutes per side until deeply browned and caramelized. For medium-rare, internal temperature should be 130-135°F. Remove to a plate and set aside.

Bring a large pot of salted water to boil. Cook rigatoni according to package directions until al dente, usually 10 to 12 minutes. Before draining, reserve ½ cup of pasta water. Drain pasta.

In the same skillet used for steak, reduce heat to medium and melt remaining tablespoon of butter. Add minced garlic and cook for 30 seconds, stirring constantly until fragrant but not browned. Pour in heavy cream and bring to a gentle simmer, scraping up browned bits from pan.

Reduce heat to low and gradually stir in Parmesan cheese, whisking constantly until melted and smooth, about 1 to 2 minutes. If using mozzarella or Fontina, add now and stir until melted. Season with ¼ teaspoon salt, black pepper, and taste. Add additional ½ to 1 teaspoon Cajun seasoning if you want more heat.

Add drained rigatoni to the sauce, tossing to coat. If sauce seems too thick, add reserved pasta water 2 tablespoons at a time. Gently fold in steak tips and any accumulated juices from the plate.

Plate immediately while hot. Garnish with extra grated Parmesan and cracked black pepper.