Bring a large pot of water to a rolling boil. Add the 8 oz elbow macaroni and cook according to the package directions, stopping 1 minute before the recommended cooking time so the pasta remains slightly firm.

Drain the macaroni thoroughly and return it to the pot. Add 1 tablespoon unsalted butter and toss until the butter has melted and evenly coated the pasta. Set aside and allow the macaroni to cool slightly.

Prepare the topping by placing the panko breadcrumbs in a small bowl with 2 tablespoons melted unsalted butter and 1/4 teaspoon salt. Stir until the crumbs are uniformly coated, then reserve the mixture for assembly.

Preheat the oven to 180°C / 350°F.

Place a large saucepan or ovenproof skillet over medium heat and melt 4 tablespoons unsalted butter. Add the all-purpose flour and stir continuously for approximately 1 minute to form a smooth roux.

Pour approximately 1 cup of the warmed milk into the roux, stirring until the flour mixture has completely dispersed. Gradually whisk in the remaining warmed milk until the sauce is smooth.

Season the mixture with 3/4 teaspoon salt, garlic powder, onion powder, and dry mustard. Continue cooking for 5 to 8 minutes, whisking regularly, until the sauce becomes thick and creamy.

Remove the sauce from the heat. Stir in the grated Gruyère and shredded mozzarella until evenly incorporated. The cheeses do not need to melt completely at this point.

Pour the prepared cheese sauce over the buttered macaroni and mix promptly until every piece of pasta is evenly coated.

Transfer the macaroni and cheese to an ovenproof skillet or baking dish. Scatter the prepared breadcrumb mixture evenly across the surface.

Bake for approximately 25 minutes, or until the topping is lightly golden and crisp. Avoid excessive baking, as prolonged oven time can cause the cheese sauce to dry out.

Serve the baked macaroni and cheese immediately.