Heat a large skillet or griddle over medium-low heat.
Butter the outside slice of each piece of bread, placing two of the buttered-sides down once the skillet is hot. Spread a bit of caramel sauce on the bread, then top with an ounce of brie cheese on both sandwiches. Add a bit more caramel, add the apple slices, and then more caramel and remaining ounce of brie for each. Spread the top piece of bread (sandwich-side down) with caramel too.
Grill or cook on each side until bread is golden brown and the cheese is melted.