01 - Preheat the oven to 425°F. Toss broccoli florets with olive oil, sea salt, and freshly ground black pepper on a baking sheet. Roast for 15 to 18 minutes until crisp and lightly browned. Remove and set aside. Reduce oven temperature to 375°F.
02 - Bring a large pot of salted water to a boil. Add macaroni and cook until al dente, about 7 to 8 minutes. Drain well and set aside.
03 - In a medium saucepan, melt the butter over medium heat. Whisk in flour and cook for 1 minute to form a roux. Gradually whisk in whole milk and continue stirring until the sauce thickens, approximately 4 to 5 minutes.
04 - Remove the saucepan from heat. Stir in sharp cheddar, Gruyère, Dijon mustard, garlic powder, ground black pepper, and kosher salt until the sauce is smooth and all cheese is fully melted.
05 - In a large mixing bowl, gently combine cooked macaroni, roasted broccoli, and cheese sauce, ensuring even coating throughout.
06 - Transfer the macaroni mixture to a well-greased 9x13-inch baking dish.
07 - In a small bowl, mix panko breadcrumbs, grated Parmesan, and melted butter. Evenly sprinkle this mixture over the macaroni and cheese.
08 - Bake in the preheated 375°F oven for 20 to 25 minutes, until the topping turns golden brown and the sauce bubbles around the edges.
09 - Allow the dish to rest for 5 minutes to set before serving.