Bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook for 1-2 minutes less than package instructions for al dente. Drain well and set aside.
Preheat your oven to 220°C (425°F). Heat a cast iron skillet over medium heat and add the butter, letting it melt until it starts to crackle and smell nutty.
Add the shredded cheddar cheese to the melted butter and stir continuously until the cheese melts into a smooth, gooey sauce. The mixture should be bubbling gently and smell richly cheesy.
Pour in the milk gradually, whisking constantly to incorporate and prevent lumps. Continue stirring until the sauce thickens slightly and becomes silky, about 2-3 minutes.
Stir the cooked pasta into the cheese sauce, tossing to coat every piece evenly. The pasta should be well-covered and glistening with cheesy goodness.
Increase the heat slightly to about 180°C (355°F) to start browning the cheese edges. Let the mixture bubble and crackle, watching for the cheese to develop golden, crispy bits around the edges. This should take about 2-3 minutes.
Sprinkle the toasted panko breadcrumbs evenly over the top, pressing them lightly into the cheesy surface. Transfer the skillet to the oven and bake for 10-12 minutes until bubbling and the top is golden brown.
Optional: Broil for 1-2 minutes to deepen the caramelization of the cheese and create extra crispy edges. Keep a close eye to prevent burning.
Remove the skillet from the oven and let it rest for 3-5 minutes. This helps the cheese set and flavors to meld, making the dish easier to serve.
Serve the mac and cheese hot, with a spoonful of crispy, caramelized cheese crust on top. Enjoy the gooey, cheesy mess with its irresistible burnt edges and crunchy topping.
