Butter one side of each bread slice generously. Place two slices butter-side down on your work surface.
Layer the brie cheese on the unbuttered side of the bread, then arrange apple slices on top. Drizzle with honey and sprinkle with thyme if using.
Top with the remaining bread slices, butter-side up.
Heat a large skillet or griddle over medium heat. Place sandwiches in the pan and cook for 3 minutes until golden brown.
Carefully flip and cook another 3 minutes until the second side is golden and the cheese is melted and gooey.
Let cool for 1 minute, slice diagonally, and serve warm.