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 just al dente, about 1–2 minutes less than package directions. Drain thoroughly 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 from heat. Stir in sharp cheddar, Gruyère, and mozzarella until completely melted and smooth. Whisk in Dijon mustard, garlic powder, onion powder, paprika, salt, and pepper. Taste and adjust seasoning as needed.
06 - Add drained macaroni to the cheese sauce, stirring until every piece is evenly coated. Transfer mixture to the prepared baking dish, spreading into an even layer.
07 - In a small bowl, combine panko breadcrumbs with melted butter and grated parmesan. Mix until evenly distributed.
08 - Sprinkle crumb mixture evenly over the macaroni. Bake uncovered for 20–25 minutes until topping is golden brown and sauce is bubbling around edges. For extra crispness, broil for 2–3 minutes at the end.
09 - Let dish stand for 5 minutes before serving to allow sauce to set slightly. Garnish with chopped fresh parsley if desired.