Preheat your oven to 350 degrees.
Choose a cast iron skillet. Just before cooking, spray the cast iron with cooking oil, or put a few drops of oil in the center and rub in it with a paper towel. This should help prevent sticking.
Add the mac & cheese to the skillet. Smooth it out with a spatula so it is in an even layer.
Bake in the oven for 25 to 35 minutes, until the cheese has browned.
Remove carefully from the oven and serve.