Bring a large pot of salted water to a boil, then add the pasta and cook until just al dente, about 8-10 minutes. Drain and set aside.
In a saucepan, melt the butter over medium heat, then whisk in the flour and cook for about 1 minute until it turns a light golden color.
Gradually pour in the milk, whisking constantly to prevent lumps, and bring to a gentle simmer. Let it thicken slightly, about 3-5 minutes.
Stir in shredded cheddar cheese, mustard powder, and a pinch of salt and pepper. Continue whisking until the cheese melts and the sauce is smooth and creamy.
Add the cooked pasta to the cheese sauce, stirring gently to coat all the pieces evenly.
Transfer the cheesy pasta mixture into a greased baking dish, spreading it out evenly.
In a small bowl, combine the panko breadcrumbs with melted butter, smoked paprika, and grated Parmesan. Spread this mixture evenly over the top of the pasta.
Bake in a preheated oven at 190°C (375°F) for 20-25 minutes, until the topping is golden brown and crispy, and the cheese is bubbling around the edges.
Once baked, remove from the oven and let it rest for about 5 minutes. This helps the cheese set slightly and makes serving easier.
Serve hot, garnished with extra herbs or cheese if desired, and enjoy the warm, cheesy, crispy goodness.