Bring a large pot of salted water to a boil and cook fettuccine according to package directions until al dente.
While pasta cooks, season steak generously with salt and pepper. Heat olive oil in a heavy cast-iron skillet over medium-high heat.
Sear steak for 3-5 minutes per side until internal temperature reaches 135°F for medium-rare. Remove from skillet and let rest for 10 minutes before slicing against the grain into thin strips.
In a large saucepan over medium heat, melt the butter. Add minced garlic and sauté for 60 seconds until fragrant.
Pour in the heavy cream and bring to a gentle simmer for 5 minutes, whisking frequently to prevent scorching.
Reduce heat to low and gradually whisk in the parmesan cheese until the sauce is smooth, creamy, and thickened.
Drain the pasta, reserving 1/4 cup of pasta water. Toss pasta immediately with the alfredo sauce, adding reserved water if needed to loosen the texture.
Divide pasta into four bowls, top with sliced steak strips, and garnish with fresh parsley.