Bring a large pot of salted water to a rolling boil and cook the pasta until al dente, about 8-10 minutes. Drain and set aside.
In the same saucepan, melt the butter over medium heat until fragrant and slightly bubbling, about 1-2 minutes. This releases a rich, toasted aroma.
Stir in the flour and whisk constantly for about 1 minute until the roux turns a light golden color and smells toasty.
Gradually pour in the milk, whisking continuously to prevent lumps. Bring to a gentle simmer and cook until the sauce thickens slightly, about 3-4 minutes, with small bubbles forming around the edges.
Stir in the mustard powder and a generous pinch of black pepper. Add the shredded cheddar cheese in small handfuls, stirring until melted and the sauce is smooth and glossy.
Add the cooked pasta into the cheese sauce, stirring well to coat every piece in that luscious, cheesy mixture.
Transfer the cheesy pasta into a greased baking dish, spreading it out evenly. Preheat your oven to 400°F (200°C).
Bake uncovered for 15-20 minutes until the top is bubbling and golden brown, with a crispy, crackly surface that signals it’s ready.
Remove from the oven and let sit for 5 minutes to settle. This rest allows the cheese to set slightly for easier serving.
Sprinkle with freshly cracked black pepper and serve hot, enjoying the bold, cheesy chaos in every bite.
