Bring a large pot of salted water to a boil and add the fettuccine, cooking according to package directions until al dente. While the pasta cooks, mince the garlic, grate the parmesan cheese, chop the fresh parsley, and drain and flake the tuna into 1/2-inch pieces. Having everything prepped and ready will allow you to work quickly once the pasta is done, which is crucial for making a silky alfredo sauce that doesn't break.

Melt the butter in a large skillet over medium heat. Add the minced garlic and salt, cooking for about 1 minute until fragrant but not browned. Reduce the heat to low and slowly pour in the room-temperature cream while stirring constantly to combine. The key here is keeping the heat low—high heat will break the sauce and make it grainy. I like to use room-temperature cream because it incorporates more smoothly without shocking the butter.

Once the cream is fully incorporated, gradually add the grated parmesan cheese a handful at a time, stirring constantly until each addition melts completely before adding more. This prevents clumping and ensures a smooth, creamy sauce. Add a pinch of nutmeg and freshly ground black pepper to taste. The sauce should be silky and coat the back of a spoon lightly.

When the pasta is finished cooking, reserve about 1/2 cup of pasta water before draining. Add the hot drained pasta directly to the alfredo sauce, stirring gently to coat. Pour in the reserved pasta water a little at a time while stirring, using it to loosen the sauce to your desired consistency—it should be creamy but not heavy. The starch in the pasta water helps the sauce cling to the noodles beautifully.

Gently fold the flaked tuna and chopped fresh parsley into the pasta and sauce, stirring just until combined and heated through—be careful not to overwork it or the tuna will break apart into tiny pieces. Taste and adjust the salt and pepper as needed. Divide among serving bowls and finish each bowl with a generous grating of fresh parmesan cheese and additional black pepper.