Bring a large pot of generously salted water to a boil and cook the fettuccine according to package directions.
During the last 3–4 minutes of pasta cooking, add the broccoli florets to the pot and cook until both pasta and broccoli are tender. Drain in a colander and return pasta and broccoli to the pot; set aside.
While the pasta cooks, melt the butter in a medium saucepan over medium heat.
Stir in the half and half and bring just to a simmer. Cook for 5–8 minutes, stirring occasionally, until the mixture slightly thickens and reduces; do not let it reach a full boil.
Add the garlic powder, salt, black pepper, cayenne, and shredded Parmesan to the sauce and stir until the cheese melts and the sauce is smooth.
Pour the Alfredo sauce over the drained fettuccine and broccoli and toss gently to coat evenly.
Serve immediately and sprinkle additional Parmesan on top if desired.