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 well 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 constantly, until mixture thickens and just starts to bubble, about 5–7 minutes.
05 - Remove from heat. Stir in cheddar, Gruyère, Dijon mustard, garlic powder, onion powder, salt, and pepper until cheese is completely melted and sauce is smooth.
06 - Add drained pasta to the cheese sauce and stir to coat evenly.
07 - Pour macaroni and cheese mixture into the prepared baking dish, spreading evenly.
08 - In a medium bowl, combine panko breadcrumbs, Parmesan cheese, and melted butter. Mix until evenly distributed.
09 - Sprinkle breadcrumb mixture evenly over the pasta. Bake for 25–30 minutes until topping is golden brown and sauce is bubbling around edges.
10 - Let rest for 5 minutes before serving to allow sauce to set. Garnish with fresh parsley if desired.