01 - Preheat oven to 350°F. Generously butter a 2-quart baking dish.
02 - Bring a large pot of salted water to a boil. Cook macaroni until al dente, about 1-2 minutes less than package directions. Drain well and set aside.
03 - In a large saucepan over medium heat, melt 3 tbsp butter. Whisk in flour and cook for 1-2 minutes, stirring constantly, until mixture is lightly golden and fragrant.
04 - Gradually pour in milk while whisking continuously to prevent lumps. Continue whisking until sauce thickens and coats the back of a spoon, about 3-5 minutes.
05 - Remove saucepan from heat. Stir in cheddar, Gruyère, and mozzarella cheeses until completely melted and smooth. Add Dijon mustard, garlic powder, onion powder, paprika, salt, and pepper. Taste and adjust seasoning as needed.
06 - Add drained macaroni to the cheese sauce. Stir thoroughly to ensure every piece is evenly coated. Transfer mixture to the prepared baking dish, spreading evenly.
07 - In a small bowl, combine panko breadcrumbs with melted butter and grated parmesan. Mix well until butter is evenly distributed.
08 - Sprinkle breadcrumb mixture evenly over the macaroni. Bake uncovered for 20-25 minutes until topping is golden brown and sauce is bubbling around edges.
09 - For extra crispiness, broil for 2-3 minutes, watching closely to prevent burning. Remove from oven and let stand 5 minutes before serving. Garnish with fresh parsley if desired.