Method:
Preheat the broiler. Bring a large pot of well-salted water to a boil. Add broccoli, return to a boil and cook, uncovered, until al dente, about 4 minutes. Remove broccoli with a slotted spoon, leaving the water in the pot. Boil the pasta in the water until just tender, about 10 minutes. Drain.
Meanwhile, melt the butter in a saucepan over medium heat. Stir in the flour and cook gently for about a minute. Whisk in the milk, salt, pepper and cayenne. Bring milk mixture to a simmer, reduce the heat, and cook for about 5 minutes until mixture thickens. Stir in two thirds of the cheese until it has melted. Remove saucepan from heat and set aside.
In 2-quart oven-proof dish, combine the pasta with 2/3 of the cheese sauce. Add the broccoli to the remaining cheese sauce in the saucepan.
Encircle the pasta in the dish with the broccoli. Sprinkle remaining cheese over the top and broil for about 3 minutes, until cheese begins to bubble.