Bring a large pot of salted water to a boil. Cook the penne 2 minutes less than the package directions suggest. Reserve ½ cup of pasta water, then drain.

While pasta cooks, season steak strips with salt and pepper. Heat olive oil in a large skillet over medium-high heat.

Add steak to the skillet in a single layer. Sear for 2 minutes per side until browned but still pink in the middle. Remove steak from the pan and set aside.

Reduce heat to medium. Add butter to the same skillet. Once melted, add minced garlic and red pepper flakes. Sauté for 1 minute until fragrant.

Add the cooked pasta and ¼ cup of the reserved pasta water to the skillet. Toss vigorously to coat the noodles in the garlic butter.

Turn off the heat. Add the steak (and any juices from the plate), Parmesan cheese, and parsley.

Toss everything together until the cheese is melted and the sauce is creamy. If it's too dry, add a little more pasta water. Serve immediately.