Cook the penne pasta according to package directions until al dente. Before draining, reserve 1 cup of pasta water, then drain and set aside without rinsing.

Pat the steak tips completely dry with paper towels and season generously with Cajun seasoning on all sides.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat until shimmering. Add the steak tips in a single layer with at least 1 inch of space between pieces. Sear for 2-3 minutes per side for medium-rare, or until a meat thermometer reads 130-135°F. Remove from the skillet, tent loosely with foil, and let rest for 3-5 minutes.

Reduce the heat to medium and add the remaining tablespoon of olive oil plus the butter to the same skillet. Once the butter melts, add the minced garlic and cook for about 1 minute until fragrant but not browned.

Whisk in the flour and cook for another minute, stirring constantly to create a smooth roux.

Gradually pour in the milk and heavy cream while whisking constantly to prevent lumps. Bring the mixture to a gentle simmer and let it cook for 3-5 minutes until it starts to thicken.

Remove the skillet from heat and stir in the grated Parmesan cheese, salt, and pepper. Keep stirring until the cheese is fully melted and the sauce is silky smooth. If the sauce looks too thick, add a splash of the reserved pasta water or milk.

Add the cooked penne and seared steak tips (along with any accumulated juices) back to the skillet with the sauce. Gently toss everything together until well coated. Garnish with fresh chopped parsley and extra Parmesan before serving.