01 - Preheat oven to 350°F and grease a 9x13 inch baking dish.
02 - Boil elbow macaroni in salted water until al dente, about 7 minutes. Drain and set aside.
03 - Melt 1/4 cup unsalted butter in a large saucepan over medium heat. Whisk in 1/3 cup all-purpose flour continuously for 2 minutes to form a smooth roux.
04 - Gradually whisk in 3 3/4 cups whole milk, stirring constantly to avoid lumps. Cook until sauce thickens, approximately 5 to 7 minutes.
05 - Incorporate 1 tsp Dijon mustard, 1/2 tsp garlic powder, 1/2 tsp onion powder, 1/2 tsp salt, and 1/4 tsp black pepper into the sauce.
06 - Remove sauce from heat and stir in 2 cups shredded sharp cheddar and 1 cup shredded Gruyère until fully melted and smooth.
07 - Mix cooked elbow macaroni with cheese sauce thoroughly, then transfer the mixture into the prepared baking dish.
08 - In a small bowl, combine 1 cup panko breadcrumbs, 2 tbsp melted unsalted butter, 1/4 cup grated Parmesan, and optional 1/4 tsp paprika. Evenly sprinkle over macaroni mixture.
09 - Bake in the preheated oven for 20 to 25 minutes until the topping is golden brown and the dish is bubbling.
10 - Allow to rest for 5 to 10 minutes before serving to set and enhance flavors.