01 - Preheat oven to 350°F. Lightly grease a 2-quart baking dish.
02 - Cook macaroni in salted boiling water until just al dente. Drain and set aside.
03 - In a large saucepan, melt 4 tbsp butter over medium heat. Stir in flour and cook for 1 minute to form a roux.
04 - Gradually whisk in milk, stirring constantly until smooth. Cook for 4-5 minutes until slightly thickened.
05 - Reduce heat to low. Add cheddar, Gruyère, Dijon mustard, garlic powder, onion powder, salt, and pepper. Stir until cheese is completely melted and sauce is smooth.
06 - Add drained macaroni to the cheese sauce and stir to coat evenly.
07 - Pour the macaroni mixture into the prepared baking dish.
08 - Combine breadcrumbs with melted butter and Parmesan cheese. Sprinkle evenly over macaroni.
09 - Bake uncovered for 25-30 minutes, until the top is golden and the edges are bubbling.
10 - Remove from oven and let stand 5 minutes. Garnish with fresh parsley before serving if desired.