01 - Preheat oven to 350°F. Grease a 2-quart baking dish.
02 - Boil salted water and cook macaroni until just al dente. Drain and set aside.
03 - Melt 4 tbsp butter in a large saucepan over medium heat. Whisk in flour constantly for 1 to 2 minutes until smooth and bubbling without browning.
04 - Gradually whisk in milk and cook, whisking frequently, until thickened and coating the back of a spoon, about 5 to 7 minutes. Stir in Dijon mustard, garlic powder, onion powder, salt, and pepper. Remove from heat.
05 - Add grated cheddar and Gruyère cheeses to the sauce. Stir until fully melted and smooth.
06 - Fold the drained macaroni into the cheese sauce until evenly coated. Transfer the mixture to the prepared baking dish.
07 - In a small bowl, mix panko breadcrumbs with melted butter and Parmesan cheese. Sprinkle evenly over the macaroni.
08 - Bake uncovered for 20 to 25 minutes until the topping is golden brown and the casserole is bubbling.
09 - Allow to rest for 5 to 10 minutes before serving to let the dish set.