Thinly slice the apple and gather all your ingredients on a clean workspace.
Butter one side of each slice of sourdough bread generously.
On the unbuttered side of one slice, layer half of the shredded cheddar cheese, followed by thin apple slices, dried cranberries, and the remaining cheese. Top with the other slice of bread, buttered side up.
Heat a skillet over medium heat and grill the assembled sandwich for about 3-5 minutes until golden brown, then flip and grill the other side for an additional 3-4 minutes.
Remove the sandwich from heat, let it cool slightly, and slice diagonally to serve.