01 - Preheat your oven to 375°F. Grease a 9x13 inch baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to a boil. Add macaroni and cook for 6 minutes. Add broccoli and cook both together for an additional 2 minutes, until pasta is just al dente and broccoli is bright green. Drain and set aside.
03 - In a large saucepan, melt 4 tbsp butter over medium heat. Stir in flour and cook for 2 minutes, stirring constantly to create a smooth roux.
04 - Gradually whisk in milk and cream. Cook, whisking continuously, until thickened and bubbling, about 5 minutes. Remove from heat and stir in cheddar, Gruyère, Dijon mustard, garlic powder, onion powder, salt, and pepper until smooth and creamy.
05 - Add cooked macaroni and broccoli to the cheese sauce. Mix until evenly coated. Pour the mixture into the prepared baking dish.
06 - In a small bowl, combine panko breadcrumbs, Parmesan cheese, and melted butter. Sprinkle evenly over the macaroni mixture.
07 - Bake for 20-25 minutes until bubbling and the top is golden brown. Let cool for 10 minutes before serving to allow the sauce to set.