Preheat the broiler.

Bring a large pot of 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.

Add pasta and cook until just tender, about 10 minutes.

Drain.

Meanwhile, melt butter in a saucepan over medium heat.

Stir in flour and cook gently for about a minute.

Whisk in milk, salt, pepper and cayenne.

Bring milk mixture to a simmer, reduce the heat, and cook until mixture thickens, about 5 minutes.

Stir in about two thirds of the cheese until it has melted.

Remove saucepan from heat and set aside.

In 2-quart oven-proof dish, combine pasta with about 2/3 of the cheese sauce.

Add broccoli to the remaining cheese sauce in the saucepan.

Place the broccoli around the edge of the dish, topping the pasta.

Sprinkle remaining cheese over the top and broil until cheese begins to bubble, about 3 minutes.