01 - Preheat the oven to 375°F. Grease a 9 x 13 inch baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to a boil. Add the macaroni and cook until al dente, about 6 minutes. Add broccoli florets during the last 2 minutes of cooking. Drain well in a colander and set aside.
03 - In a medium saucepan, melt 4 tbsp butter over medium heat. Add flour and whisk constantly for 1-2 minutes, until the mixture bubbles and turns slightly golden but does not brown.
04 - Gradually whisk in the whole milk until smooth and no lumps remain. Add Dijon mustard, garlic powder, onion powder, black pepper, and salt. Cook, stirring frequently, until the sauce thickens and just begins to bubble, 5-7 minutes.
05 - Remove the saucepan from heat. Stir in the sharp cheddar and Gruyère cheeses until completely melted and the sauce is smooth and creamy.
06 - Add the cooked pasta and broccoli to the cheese sauce. Mix thoroughly until all components are evenly coated. Transfer the mixture to the prepared baking dish, spreading it into an even layer.
07 - In a small bowl, combine the fresh breadcrumbs with melted butter and grated Parmesan cheese. Mix until the breadcrumbs are evenly moistened.
08 - Sprinkle the breadcrumb mixture evenly over the macaroni and cheese. Bake for 20-25 minutes, or until the topping is golden brown and the sauce is bubbling around the edges.
09 - Remove from the oven and let the dish stand for 5 minutes before serving. This allows the sauce to set slightly for easier serving.