In a bowl, beat the softened butter, grated Parmesan, and garlic powder with a hand mixer until smooth and creamy.
Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente, about 12 minutes.
Reserve 1/2 cup of the pasta cooking water, then drain the pasta in a colander.
Return the hot pasta to the warm pot. Add 1/2 teaspoon salt, the cheese-butter mixture, and 1/4 cup of the reserved pasta water.
Toss the pasta vigorously, adding more reserved pasta water as needed to create a smooth, silky sauce that coats the noodles.
Serve immediately with additional grated Parmesan if desired.