01 - Preheat oven to 425°F. Toss broccoli florets with olive oil, sea salt, and fresh black pepper on a baking sheet. Roast for 15 to 18 minutes until crisp and lightly browned. Remove and set aside. Lower oven temperature to 375°F.
02 - Cook elbow macaroni in a large pot of salted boiling water until al dente, about 7 to 8 minutes. Drain and set aside.
03 - In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 1 minute. Gradually whisk in whole milk and cook until sauce thickens, approximately 4 to 5 minutes.
04 - Remove sauce from heat. Stir in sharp cheddar, Gruyère, Dijon mustard, garlic powder, ground black pepper, and kosher salt until cheese melts fully and sauce is smooth.
05 - In a large mixing bowl, gently fold together the cooked macaroni, roasted broccoli, and cheese sauce until evenly coated.
06 - Transfer the macaroni mixture to a greased 9x13-inch baking dish.
07 - In a small bowl, combine panko breadcrumbs, grated Parmesan, and melted butter. Sprinkle evenly over the macaroni mixture.
08 - Bake uncovered at 375°F for 20 to 25 minutes until the topping is golden brown and the sauce is bubbling.
09 - Allow to rest for 5 minutes before serving for best texture.