Mix the butter with the sriracha and, if using, the chili flakes in a small bowl.
1 teaspoons softened butter, 1 teaspoon sriracha, 1 teaspoon chili flakes
Butter one slice of bread with plain butter then turn the bread over and butter the other side with the Sriracha butter. Add the cheese, apple slices, and more cheese. Top with the other piece of bread then butter the top.
4 slices bread, 4 ounces cheese, ½ apple
Heat a small frying pan over medium-low heat. Add the sandwich and cover the pan. Cook for 2-3 minutes on each side, until the cheese has melted, and the bread is brown and crispy. Enjoy!