In a large pot, bring 6 cups of water to a rolling boil. Add 1 tablespoon kosher salt. Add 12 oz dry fettuccine and cook uncovered according to package instructions until al dente (typically 10–12 minutes). Reserve 1 cup of pasta cooking water, then drain the pasta and set aside.

Season salmon

While pasta cooks, pat 12 oz salmon fillets dry with paper towels. Season both sides with 1/2 teaspoon black pepper and a pinch of salt (use sparingly because sauce and pasta water are salty).

Pan-sear salmon

Heat 1 tablespoon olive oil in a nonstick or stainless steel skillet over medium-high heat until shimmering. Add salmon fillets and sear 3–4 minutes per side (depending on thickness) until golden and just cooked through (internal temperature ~125–130°F for medium). If salmon is thin, reduce time to 2–3 minutes per side. Remove salmon to a plate and let rest 3 minutes, then flake into large chunks. If using lemon, squeeze 1/2 lemon over salmon now.

Alfredo Sauce

Melt butter and sauté garlic

In a large sauté pan or skillet over medium heat, melt 4 tablespoons unsalted butter. Add 2 cloves minced garlic and cook, stirring, until fragrant but not browned, about 30–45 seconds.

Add cream and milk

Pour in 1 cup heavy cream and 1/2 cup whole milk. Stir to combine and bring to a gentle simmer over medium-low heat. Do not boil; maintain a gentle simmer for 3–4 minutes to slightly reduce and thicken.

Incorporate cheese and season

Lower heat to low. Gradually whisk in 1 cup freshly grated Parmesan cheese a little at a time until melted and sauce is smooth. Season with 1/2 teaspoon salt, 1/4 teaspoon freshly ground black pepper, and 1/8 teaspoon nutmeg (optional). If the sauce becomes too thick, whisk in reserved pasta cooking water, 1–2 tablespoons at a time, until you reach a smooth, silky consistency that will coat the pasta (you may need 2–4 tablespoons).

Combine pasta and sauce

Add the drained fettuccine to the skillet with the Alfredo sauce. Toss gently with tongs or two forks over low heat for 1–2 minutes so the pasta absorbs the sauce. If needed, add more reserved pasta water (up to 1/2 cup) to loosen the sauce and achieve desired creaminess.

Add salmon and finish

Gently fold the flaked salmon into the sauced fettuccine, being careful not to break the pieces too small. Warm together for 1 minute just to integrate flavors. Taste and adjust seasoning with salt and pepper if necessary.

Garnish and serve

Plate the fettuccine Alfredo topped with salmon. Sprinkle 2 tablespoons chopped fresh parsley and an extra dusting of Parmesan if desired. Serve immediately with lemon wedges on the side.