In a medium saucepan, cook macaroni according to package directions, until slightly firm. Drain well.
Cook the broccoli following package directions, on the stovetop or in the microwave.
Preheat oven to 375° F. Grease a 2-quart baking dish.
In a medium saucepan, melt butter. Add flour, stirring for about 1 minute, until
smooth and bubbly. Gradually whisk in milk, stirring constantly until thickened,
about 3 minutes, remove from heat.
Reserve 1/2 cup cheddar cheese and 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 longer, until lightly browned and bubbly.
Serves 4 to 6
Calories per serving (based on 6 sersvings): 415
Fat per serving (based on 6 sersvings): 20.5g