Preheat the oven to 400°F (200°C) with a rack in the center position.

Bring a large pot of salted water to a boil. Cook the elbow macaroni until 1 minute before al dente according to package instructions. Drain and set aside.

In a large Dutch oven or braiser, melt ½ cup butter over medium heat.

Add the flour and stir continuously for 1–2 minutes until a thick roux forms.

Slowly whisk in the milk, stirring constantly until smooth and creamy.

Reserve 1½ cups of cheddar cheese. Add the remaining cheese to the sauce along with 2 teaspoons salt, garlic powder, mustard powder, and black pepper. Stir until the cheese melts and the sauce becomes thick and smooth.

Stir the cooked macaroni into the cheese sauce until evenly coated.

In a small saucepan, melt the remaining ¼ cup butter. Remove from heat and toss with the panko breadcrumbs.

Transfer the macaroni mixture to a baking dish. Sprinkle the reserved cheese and the buttered panko topping evenly over the top.

Bake for 20–25 minutes, until golden and bubbling.

Garnish with parsley before serving if desired.