Preheat the oven to 350°F (175°C) and butter or oil a medium baking dish.
Bring a large pot of water to a boil, season generously with Kosher Salt, and cook the Elbow Macaroni until just al dente; drain and set aside.
In a medium saucepan over medium heat, melt 2–3 tablespoons of Unsalted Butter, then whisk in an equal amount of All-Purpose Flour and cook for about 1–2 minutes to form a light roux without browning.
Slowly pour in the Whole Milk while whisking constantly, then simmer gently until the mixture thickens into a smooth sauce, about 4–6 minutes.
Remove the pan from the heat and stir in shredded Sharp Cheddar Cheese until melted and smooth; season with freshly ground Black Pepper, a pinch of Dry Mustard for brightness, and a dusting of Paprika for color. Taste and add more Kosher Salt if needed.
Fold the cooked macaroni into the cheese sauce until evenly coated, then transfer everything to the prepared baking dish.
Sprinkle the top evenly with Breadcrumbs and dot with a few small pieces of the remaining Unsalted Butter so the topping crisps and browns nicely in the oven.
Bake until the top is golden and the sauce is bubbling around the edges, about 20–25 minutes. Let rest for 5 minutes before serving so the sauce sets slightly.
