Heat a frying pan over medium heat.
Spread 1/2 tbsp butter on each slice of toast.
Place one piece, butter side down, on the pan.
Sprinkle half of the cheese, then spread the mac & cheese (recipe HERE), and then sprinkle the rest of the cheese.
Place the second piece of bread on butter side up.
Place a lid on top and flip once the bottom is golden brown. Once the second side is golden brown, cut in half and serve!