In a large pot, bring salted water to a boil. Add the pasta and cook according to package instructions until al dente. Reserve 1/2 cup of pasta water, then drain the pasta and set aside.

In a large skillet, heat olive oil over medium-high heat. Add the sliced steak and season with salt and pepper. Cook for about 3-4 minutes, stirring occasionally, until the steak is browned and cooked to your desired doneness. Remove the steak from the skillet and set aside.

In the same skillet, add the minced garlic and red pepper flakes (if using). Sauté for about 1 minute until fragrant, being careful not to burn the garlic.

Pour in the heavy cream and bring to a gentle simmer. Cook for 2-3 minutes, stirring frequently, until the cream thickens slightly.

Stir in the grated Parmesan cheese until melted and smooth. If the sauce is too thick, add a little reserved pasta water to reach your desired consistency.

Add the cooked pasta and seared steak to the skillet with the sauce. Toss everything together until well coated.

Serve immediately, garnished with chopped fresh parsley.