Sear the Steak: Heat 1 tablespoon of butter in a large skillet over medium-high heat. Add the steak, season with salt and pepper, and sear for 2–3 minutes per side until browned. Remove steak and set aside.

Sauté the Garlic: In the same skillet, reduce heat to medium and add the remaining butter. Stir in garlic and crushed red pepper flakes. Cook for 1–2 minutes until fragrant.

Build the Sauce: Pour in the heavy cream and stir to combine, scraping up browned bits from the pan. Let the sauce simmer for 3–4 minutes to thicken. Stir in Parmesan and cook until melted.

Cook the Pasta: Add the rotini pasta, then pour in enough water or broth to cover. Bring to a boil, then reduce heat and simmer, covered, for 10–12 minutes, stirring occasionally, until pasta is al dente.

Combine Everything: Return steak to the skillet, toss everything together, and cook for an additional 2–3 minutes to heat through. Adjust seasoning to taste.

Garnish & Serve: Top with chopped parsley and extra Parmesan if desired. Serve hot.