01 - Preheat oven to 350°F. Grease a 9x13 inch baking dish.
02 - Bring a large pot of salted water to a boil. Add macaroni and cook 4 minutes less than package directions. Add broccoli florets during the last 2 minutes. Drain and set aside.
03 - In a medium saucepan over medium heat, melt 4 tablespoons butter. Whisk in flour and cook for 1 minute.
04 - Gradually whisk in milk, stirring constantly until smooth and slightly thickened, about 5 minutes. Stir in Dijon mustard, garlic powder, onion powder, salt, and black pepper. Remove from heat.
05 - Add cheddar, mozzarella, and Parmesan cheeses to the sauce. Stir until completely melted and smooth.
06 - Mix the cooked macaroni and broccoli with the cheese sauce. Transfer the mixture to the prepared baking dish.
07 - In a small bowl, combine panko breadcrumbs, melted butter, and Parmesan cheese. Evenly sprinkle over the macaroni mixture.
08 - Bake for 25 to 30 minutes until topping is golden brown and the dish is bubbling. Let rest for 5 minutes before serving.