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