Cook the pasta: Boil the pasta in salted water according to the package directions until al dente. Drain and set aside.

Sear the steak: Pat the steak dry and season with 1/2 teaspoon of the salt and the pepper. Heat the olive oil and 1 tablespoon of the butter in a large skillet over high heat until shimmering. Sear the steak in a single layer for 2-3 minutes per side, until a meat thermometer reads 130-135°F for medium-rare. Transfer to a plate and tent with foil.

Build the base: Reduce the heat to medium and melt the remaining 3 tablespoons of butter in the same skillet. Add the garlic and cook for 30 seconds until fragrant.

Make the roux: Sprinkle in the flour and stir constantly for 1 minute, then slowly whisk in the chicken broth, scraping up the browned bits left from searing the steak.

Add the cream and parmesan: Stir in the heavy cream, remaining 1/2 teaspoon salt, and red pepper flakes if using. Simmer for 2-3 minutes until slightly thickened, then reduce the heat to low and stir in the parmesan until smooth.

Combine: Add the cooked pasta to the skillet and toss to coat in the sauce.

Return the steak: Stir the seared steak and any accumulated juices back into the pasta, tossing gently just to warm through.

Garnish and serve: Sprinkle with fresh parsley and serve right away.