In a medium saucepan, cook macaroni according to package directions, until
al dente, or still slightly firm. Drain well.
Fill another saucepan 3/4 full with water. Bring water to a boil, add
broccoli, reduce heat to medium and cook until al dente; Drain and set
aside.
Preheat oven to 375°. Grease an 8 x 8 inch glass baking dish.
In a medium saucepan, melt butter. Add flour, stirring 1 minute, until
smooth. Gradually whisk in milk, stirring continually until thickened,
about 3 minutes, remove from heat.
Reserve 1/2 cup cheddar cheese. Stir remaining cheddar, Gruyere,
Parmesan, salt, and cayenne into sauce until cheeses melt. Add macaroni
and broccoli to sauce. Pour into prepared baking dish.
Bake 15 minutes. Sprinkle top with reserved cheddar and bread crumbs.
Bake 10 to 15 minutes, until bubbly.
Serves 4.