Bring a medium pot of salted water to a boil and cook 2 ounces fettuccine according to package directions until al dente; drain and set aside.
While the pasta is finishing, 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 pepper, and a pinch of cayenne (optional). Heat until steaming but not boiling.
Reduce heat to low and stir in 1/2 ounce shredded Parmesan until fully melted and the sauce is smooth.
Toss the drained fettuccine with the sauce until evenly coated, then let sit for about 5 minutes to thicken slightly.
Adjust seasoning if needed, garnish with fresh parsley if desired, and serve.