Preheat your oven to 200°C (390°F) and lightly butter your baking dish.
Bring a large pot of salted water to a boil, then cook the pasta until just al dente, about 8 minutes. Drain and toss with a splash of olive oil to prevent sticking.
While the pasta cooks, melt 2 tablespoons of butter in a saucepan over medium heat. Once melted and shimmering, add the flour and whisk continuously for about 1 minute until it forms a smooth paste.
Slowly pour in the milk while whisking constantly to prevent lumps. Bring the mixture to a gentle simmer and cook until slightly thickened, about 3-4 minutes, with a gentle bubbling sound.
Add the shredded cheddar cheese and mustard powder to the sauce, stirring until the cheese is fully melted and the sauce is smooth and creamy. Season generously with salt and pepper.
Fold the cooked pasta into the cheese sauce using a spatula until evenly coated. Transfer the cheesy pasta mixture into your prepared baking dish.
In a small skillet, melt 2 tablespoons of butter and toast the panko breadcrumbs until golden and crispy, about 3-4 minutes. Sprinkle the toasted breadcrumbs evenly over the pasta.
Bake the assembled dish in the preheated oven for 20-25 minutes, until bubbling around the edges and the top is golden brown.
Remove from oven and let rest for 5 minutes. This helps the cheese sauce settle and makes serving easier.
Serve hot, spooning out generous portions with a crispy top and gooey center—perfect for savoring every cheesy bite.
