Bring a large pot of salted water to a boil and cook penne according to package directions until 1 minute shy of al dente. Drain and set aside, reserving 1/4 cup pasta water.
Season sliced steak strips generously with salt and black pepper.
Heat olive oil and 1 tablespoon butter in a large skillet over high heat until shimmering.
Add steak strips in a single layer and sear for 2 minutes without moving, then flip and sear for another 1 to 2 minutes until browned. Transfer steak to a plate.
Reduce heat to medium, add remaining 2 tablespoons butter and minced garlic to the pan, cooking for 1 minute until fragrant.
Pour in beef broth to deglaze the skillet, scraping up any browned bits from the bottom.
Add cooked penne and reserved pasta water to the skillet, tossing for 1 to 2 minutes until sauce coats the pasta.
Stir in Parmesan cheese, return seared steak to the skillet, and toss everything together to warm through.
Top with chopped parsley and red pepper flakes before serving immediately.