Start by making your favorite macaroni and cheese recipe. Don't be afraid to get creative. Gibson's version changes regularly; the American makes use of leftover cheese pieces and bacon scraps.
Once you've made the macaroni and cheese, spread it in an even layer on a cookie sheet that has been sprayed with cooking spray. Let cool.
Once the macaroni and cheese is cold, slice it into squares that are roughly 1/2-inch smaller than the bread you plan on using for the grilled cheese.
Preheat the oven to 500°F and place a cast-iron skillet (or other oven-proof pan) inside.
To assemble the sandwich, butter one side of two slices of bread with salted butter. Gibson likes salted butter because it makes the sandwich have a nice salty crust.
Place the bread, buttered side down on a work surface and top one piece with a slice of cheese, the macaroni and cheese square, and another slice of cheese. The cheese slices act as glue for the sandwich, ensuring that the macaroni and cheese doesn't fall out. Cover the second piece of cheese with the remaining slice of bread, butter side out.
Remove the skillet (or pan) from the oven and place the sandwich inside.
Bake in the oven for 1-2 minutes, until the cheese is completely melted, the bread is toasted, and the macaroni and cheese is hot. Slice into triangles and enjoy immediately.
