Boil penne in salted water until al dente (10–11 mins). Reserve ½ cup water, drain, and set aside.
Toss steak tips with olive oil, Cajun seasoning, garlic powder, paprika, salt, and pepper.
Sear steak in a hot skillet for 3–4 mins per side. Add butter in the last minute to baste. Remove and set aside.
Lower heat. Melt butter in the same skillet and cook garlic for 1 minute.
Add cream and milk. Stir in cream cheese until smooth.
Mix in mozzarella, Parmesan, and Cajun seasoning. Cook until thick. Use pasta water if needed to thin.
Add pasta and steak to the sauce. Gently fold and simmer 2–3 minutes.
Garnish with parsley. Optional: top with cheese and broil 2–3 mins until bubbly.