Bring a large pot of salted water to a boil, then add the elbow macaroni and cook until just under al dente, about 2 minutes less than package instructions. Drain and set aside.
In a saucepan, melt the butter over medium heat until it starts to sizzle and smell toasty. Add the flour and whisk continuously for about 1 minute until the mixture turns light golden.
Slowly pour in the milk and heavy cream, whisking constantly to prevent lumps. Bring the mixture to a gentle simmer, and cook for 3-4 minutes until it thickens slightly and coats the back of a spoon.
Lower the heat and stir in the shredded cheddar cheese, mustard powder, and cayenne pepper. Keep stirring until the cheese has melted into a smooth, cheesy sauce with a bubbling, gooey texture.
Add the cooked pasta directly into the cheese sauce and stir well to coat every piece. The sauce should be thick, cheesy, and slightly sticky—adjust seasoning with hot sauce if you like extra heat.
Transfer the cheesy pasta mixture into a greased baking dish. Spread evenly and sprinkle the toasted breadcrumbs over the top for a crunchy crown.
Dot the top with a few small knobs of butter for extra richness, then bake in a preheated oven at 200°C (390°F) for 15-20 minutes until bubbling and golden brown on top.
Remove from the oven and let rest for about 5 minutes—this helps the cheese sauce to set slightly and makes serving easier.
Slice and serve hot, with a sprinkle of extra cheese or hot sauce if desired. The dish should be gooey, cheesy, with a crispy topping, and full of bold, chaotic flavors.
