01 - Preheat oven to 350°F. Butter a 2-quart baking dish thoroughly.
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 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 until lightly golden, stirring constantly.
04 - Gradually add milk, whisking constantly to prevent lumps. Continue whisking until sauce thickens, about 3–5 minutes.
05 - Remove from heat. Stir in cheddar, Gruyère, and mozzarella until completely 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 until evenly coated. Pour mixture into the prepared baking dish.
07 - In a small bowl, mix panko with melted butter and parmesan until well combined. Sprinkle evenly over the macaroni.
08 - Bake uncovered for 20–25 minutes until golden brown and bubbling. Broil for 2–3 minutes for extra crispiness if desired.
09 - Let stand for 5 minutes before serving. Garnish with fresh parsley if using.