Preheat your oven to 180°C (355°F) and set a large pot of salted water to boil.
Add the elbow macaroni to the boiling water and cook until al dente, about 8 minutes. Stir occasionally to prevent sticking.
Drain the pasta, reserving a cup of the pasta water, and set aside.
In a saucepan, melt the butter over medium heat until it starts to foam softly, releasing a rich aroma.
Add the flour to the melted butter and whisk continuously for about 1 minute until the mixture turns slightly golden and smooths out, creating a roux.
Gradually pour in the milk while whisking constantly, making sure to incorporate fully to avoid lumps. Continue whisking until the sauce thickens and coats the back of a spoon, about 3-5 minutes.
Stir in the shredded cheddar and Parmesan cheeses, mixing until fully melted and the sauce is smooth. Add a pinch of cayenne pepper, salt, and pepper to taste, then remove from heat.
Combine the cooked pasta with the cheese sauce in a large bowl, adding a splash of reserved pasta water if needed to loosen the sauce and ensure it’s creamy.
Transfer the cheesy pasta mixture into a buttered baking dish, spreading it evenly with a spatula.
Sprinkle the toasted breadcrumbs over the top, along with a little extra cheese if desired, to create a crispy topping.
Bake uncovered in the oven for 20-25 minutes until bubbling around the edges and golden on top, filling your kitchen with a warm, cheesy aroma.
Remove from the oven and let it sit for a few minutes before serving, allowing the cheese to set slightly and the dish to cool just enough to enjoy that perfect gooey, crunchy contrast.
