Prep the Ingredients: Start by removing the rind from the Brie cheese and slicing it into thick pieces. Core and thinly slice the apple into wedges. If using fresh thyme, rinse and pat dry the leaves.
Assemble the Sandwich: Lay one slice of sourdough bread on a clean work surface. Spread one tablespoon of softened butter on one side. On the unbuttered side, layer half of the Brie slices followed by the apple slices and a drizzle of cranberry sauce. If you're using thyme, sprinkle it on top, then season with a pinch of salt and pepper. Finish by adding the remaining Brie slices. Place the second slice of bread on top, buttered side facing out.
Grill the Sandwich: Heat a skillet over medium heat. Once hot, add the sandwich carefully. Cook for about 3-4 minutes on one side or until golden brown and the cheese begins to melt.
Flip and Finish: Using a spatula, carefully flip the sandwich and grill for another 3-4 minutes on the other side, pressing gently down with the spatula to ensure even cooking.
Serve: Once both sides are golden brown and the cheese is fully melted, remove from the skillet. Allow it to cool for a minute before slicing in half. Serve warm and enjoy the melty goodness with a side of extra cranberry sauce for dipping if desired!