01 - Preheat oven to 350°F. Grease a 2-quart baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to a boil. Add macaroni and cook until just al dente, about 1–2 minutes less than package instructions. Drain thoroughly and set aside.
03 - In a large saucepan, melt 4 tbsp butter over medium heat. Whisk in flour and cook, stirring constantly, for 1–2 minutes until foamy but not browned.
04 - Gradually whisk in the milk and heavy cream. Cook, whisking continuously, until mixture thickens and just starts to bubble, about 5–7 minutes.
05 - Remove from heat. Stir in sharp cheddar, Gruyère, Dijon mustard, garlic powder, onion powder, salt, and pepper until cheese is completely melted and sauce is silky smooth.
06 - Add drained pasta to the cheese sauce. Stir gently but thoroughly to coat every piece of macaroni evenly.
07 - Pour the macaroni and cheese mixture into the prepared baking dish, spreading evenly.
08 - In a small bowl, combine panko breadcrumbs, grated Parmesan, and melted butter. Mix until butter is evenly distributed.
09 - Sprinkle the breadcrumb mixture evenly over the pasta surface.
10 - Bake for 25–30 minutes until topping is deep golden brown and sauce is bubbling around the edges.
11 - Let rest for 5 minutes before serving to allow sauce to set. Garnish with fresh parsley if desired.