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 and set aside.
03 - In a large saucepan over medium heat, melt 3 tbsp butter. Whisk in flour and cook for 1–2 minutes until lightly golden, stirring constantly.
04 - Gradually add milk, whisking constantly to avoid lumps. Continue whisking until sauce thickens, about 3–5 minutes.
05 - Remove from heat. Stir in cheddar, Gruyère, and mozzarella until melted and smooth. Add Dijon, garlic powder, onion powder, paprika, salt, and pepper. Taste and adjust seasoning as needed.
06 - Add drained macaroni to the cheese sauce, stirring to evenly coat all pasta. Pour mixture into the prepared baking dish.
07 - In a small bowl, mix panko with melted butter and parmesan until combined. Sprinkle evenly over the macaroni.
08 - Bake uncovered for 20–25 minutes until topping is golden and sauce is bubbling around edges. For extra crispness, broil for 2–3 minutes at the end, watching closely.
09 - Let stand for 5 minutes before serving to allow sauce to set. Garnish with chopped parsley if desired.