Mince the garlic, grate the Parmesan cheese, and measure out the heavy cream and milk; set aside.

Fill a large pot with water, bring to a rolling boil over high heat, add a generous pinch of salt, and maintain boiling.

Remove steaks from the refrigerator 10 minutes before cooking, pat dry, season both sides with kosher salt and freshly ground black pepper.

Heat a cast iron skillet over medium-high heat, add 1 tablespoon butter, and when melted, sear steaks for 4 to 5 minutes without moving.

Flip steaks, add remaining 1 tablespoon butter, and cook for 3 to 4 minutes more until internal temperature reaches 130–135°F, then transfer to a plate and tent with foil to rest for 5 minutes.

Add fettuccine to the boiling water and cook 8 to 10 minutes until al dente, stirring occasionally; reserve 1 cup pasta water, then drain.

In a large skillet over medium heat, melt 4 tablespoons butter, add minced garlic, and cook for 30 to 45 seconds until fragrant; pour in heavy cream and milk and bring to a gentle simmer.

Reduce heat to medium-low, gradually whisk in Parmesan cheese a handful at a time until smooth, then season with nutmeg, salt, and white pepper.

Add drained pasta to the sauce, toss gently, and add reserved pasta water 1/4 cup at a time until the sauce coats the pasta evenly; adjust seasoning as needed.