Bring a medium pot of salted water to a boil and cook 2 ounces fettuccine according to package directions until al dente; reserve a small splash of pasta water if desired, then drain and set aside.
While the pasta cooks, melt 1 tablespoon butter in a small saucepan over medium heat.
Stir in 1/3 cup half and half (or milk or cream), 1/8 teaspoon garlic powder, a pinch of dried parsley (optional), a pinch of salt, a pinch of black pepper, and a pinch of cayenne (optional). Heat until the mixture is steaming but not boiling.
Reduce heat to low and stir in 1/2 ounce shredded Parmesan until fully melted and the sauce is smooth; add a splash of reserved pasta water if needed to loosen the sauce.
Toss the drained fettuccine with the sauce until evenly coated, then let sit about 5 minutes for the sauce to thicken slightly before serving.
Garnish with additional parsley if desired and enjoy.
