Fill a large pot with salted water and bring it to a boil. Add the elbow macaroni, cooking until al dente, about 7-8 minutes. Drain and set aside.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Whisk in the all-purpose flour, cooking for 2 minutes until a smooth roux forms.

Gradually pour in the whole milk while whisking continuously. Keep stirring until the mixture thickens and is creamy, about 5-7 minutes.

Stir in the Dijon mustard, garlic powder, salt, and pepper.

Add the cream cheese to the thickened mixture; stir until fully melted. Then, mix in the sharp cheddar and Gruyère cheeses until the sauce is smooth.

Fold the cooked elbow macaroni into your cheesy sauce, ensuring each piece is well-coated.

In a separate bowl, mix the remaining 2 tablespoons of melted butter with the panko breadcrumbs until evenly coated.

Pour the macaroni and cheese mixture into a greased baking dish, spreading it out evenly. Sprinkle the buttery panko mixture generously over the top.

Place in a preheated oven at 375°F (190°C) and bake for 20-25 minutes, or until the top is golden brown and crispy.

Allow the mac and cheese to rest for 5 minutes before serving. Sprinkle with freshly chopped parsley if desired.