Cook the fettuccine pasta according to the package directions until al dente. Drain and set aside.

In a large skillet, melt the butter over medium heat. Add the flour and whisk to combine. Cook the flour and butter together for 30–60 seconds, then slowly add the milk. Add the milk a small amount at a time, whisking well between each addition.

Cut the cream cheese into small chunks and add them to the sauce, stirring until melted and fully incorporated.

Add the freshly grated Parmesan cheese, chopped parsley, garlic powder, onion powder, salt, and pepper. Whisk until smooth and well combined.

Gently stir in the lump crabmeat and allow the sauce to cook on low heat until the crab is heated through.

Toss the cooked fettuccine with the sauce until evenly coated, or serve the pasta topped with the sauce.