Preheat your oven to 191 °C (190 °C). Cook the macaroni according to package directions until al dente. Drain well and return the pasta to the pot. Stir in 45 ml of butter to coat the pasta and prevent sticking. Set aside.

In a large saucepan or Dutch oven, melt the remaining 60 ml of butter over medium heat. Whisk in the flour and cook for 1-2 minutes, stirring constantly, to create a blonde roux.

Gradually whisk in the milk, about one cup at a time, ensuring each addition is incorporated before adding the next. Continue whisking until the sauce is smooth and lump-free.

Bring the sauce to a gentle simmer, stirring frequently, and cook for 5-7 minutes, or until it has thickened enough to coat the back of a spoon.

Remove the saucepan from the heat. Stir in the grated cheddar and Gruyere cheeses, salt, pepper, smoked paprika, and garlic powder until the cheese is fully melted and the sauce is smooth.

Pour the cheese sauce over the cooked macaroni and stir gently to combine, ensuring all the pasta is well-coated.

Transfer the macaroni and cheese mixture to a greased 9x13 inch baking dish. In a small bowl, combine the Panko breadcrumbs with the 60 ml of melted butter. Sprinkle this mixture evenly over the top of the macaroni.

Bake for 20-25 minutes, or until the topping is golden brown and the sauce is bubbly around the edges. Let stand for 5-10 minutes before serving.