Preheat the oven to 400°F / 205°C and grease a 9 × 13in / 23 × 33cm baking dish. Measure 6 tablespoons of unsalted butter.
Cook 450g of elbow macaroni in salted boiling water for 1-2 minutes less than the package time. Drain and stir in a third of the butter.
Melt another third of the butter in a large saucepan over medium heat. Whisk in 3 tablespoons of all-purpose flour and cook for 1 minute, then slowly whisk in 3 cups of whole milk.
Once simmering, stir in 3½ cups of shredded cheddar until melted, then ½ teaspoon of salt, ½ teaspoon of ground mustard, ½ teaspoon of smoked paprika, and ½ teaspoon of garlic powder.
Pour the sauce over the pasta, add 85g of full-fat block cream cheese, and stir until smooth. Spread in the baking dish.
Melt the remaining butter, toss with 1 cup of panko, and sprinkle over the top. Bake for 30 minutes, until lightly browned and bubbling at the sides, covering loosely with foil halfway through.
