01 - Bring a large pot of salted water to a rolling boil. Add elbow macaroni and cook until just al dente, about 7–8 minutes. Drain and set aside.
02 - In a heavy-bottomed saucepan over medium heat, melt butter. Add flour, whisking continuously to form a roux. Cook for 1–2 minutes, then gradually pour in milk while whisking. Bring to a gentle simmer until thickened, about 5 minutes.
03 - Remove sauce from heat. Stir in salt, black pepper, and mustard powder. Add cheddar and mozzarella cheese, whisking until fully melted and smooth.
04 - Fold macaroni into cheese sauce, ensuring all pasta is well coated. Transfer mixture into a greased 9x13 inch baking dish.
05 - Mix panko breadcrumbs with melted butter, grated parmesan, and smoked paprika. Evenly sprinkle topping over macaroni mixture.
06 - Bake at 375°F (190°C) for 25–30 minutes or until topping is golden brown and cheese is bubbling at the edges.
07 - Let stand for 10 minutes before portioning to allow the dish to set.