Bring a large pot of salted water to a boil. Cook the fettuccine according to package directions until al dente. Reserve 1 cup of pasta water before draining.
In a large skillet over medium heat, melt the butter. Add the heavy cream and bring to a gentle simmer. Cook for 2-3 minutes, stirring constantly, until slightly thickened.
Reduce heat to low. Gradually whisk in the grated Parmesan until smooth and creamy. Stir in garlic powder, salt, and pepper. If too thick, add a splash of reserved pasta water.
Add the drained pasta to the skillet. Toss to coat evenly, adding more pasta water if needed for a silky consistency. Serve immediately garnished with parsley and extra cheese.