Spread the butter on one side of two slices of the bread and place them, butter-side down, into the skillet.
As the bread cooks, drizzle each with a 1/2 tablespoon of caramel. Divide half of the brie between the two bread slices, add another 1/2 tablespoon of caramel, the apple, the remaining caramel and finally the rest of the cheese.
Butter one side of the remaining bread slices and place on top.
Flip sandwich once the bottom slices are well browned.
Continue cooking until the bread is browned and crispy and the cheese has melted. You might find that the cheese melts better if you put a lid over the skillet while cooking.