01 - Preheat the oven to 375°F. Grease a 9 x 13-inch baking dish.
02 - Bring a large pot of salted water to a boil. Add macaroni and cook for 5 minutes. Add broccoli florets and cook an additional 2 to 3 minutes until pasta is al dente and broccoli is tender. Drain thoroughly.
03 - In a large saucepan, melt 4 tablespoons of butter over medium heat. Whisk in flour and cook, stirring constantly, for 1 to 2 minutes.
04 - Gradually whisk in whole milk and heavy cream. Continue to whisk until the sauce thickens and bubbles, about 4 to 5 minutes. Remove from heat and stir in sharp cheddar, mozzarella, Parmesan cheeses, Dijon mustard, garlic powder, onion powder, salt, and black pepper until smooth.
05 - Mix the drained macaroni and broccoli gently with the cheese sauce, ensuring even coating. Transfer the mixture to the prepared baking dish.
06 - In a small bowl, combine panko breadcrumbs, melted butter, and Parmesan cheese. Sprinkle evenly over the macaroni mixture. Bake for 20 to 25 minutes until the top is golden and the sauce is bubbling.
07 - Let the dish rest for 5 minutes before serving. Garnish with chopped fresh parsley if desired.