01 - Preheat oven to 350°F. 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, until sauce thickens, about 3–5 minutes. Remove from heat.
05 - 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. Pour mixture into the prepared baking dish.
07 - In a small bowl, mix panko with melted butter and parmesan. Sprinkle evenly over the macaroni.
08 - Bake uncovered for 20–25 minutes, until golden and bubbling. Broil for 2–3 minutes for extra crispness if desired.
09 - Let stand 5 minutes before serving. Garnish with parsley if using.