In a bowl, beat the softened butter, grated Parmesan, and garlic powder with a hand mixer until smooth and creamy; set aside.
Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente, about 12 minutes.
Before draining, reserve about 1/2 cup of the pasta cooking water, then drain the pasta in a colander.
Return the drained fettuccine to the warm pot, add 1/2 teaspoon salt, the cheese-butter mixture, and 1/4 cup of the reserved pasta water; toss to combine into a creamy sauce.
Add more reserved pasta water, a tablespoon at a time, as needed to reach desired sauce consistency, then serve with additional Parmesan.