Melt 1 tablespoon of butter in a small skillet over medium heat.
Add the apple slices and salt, sautéing for 3 minutes until the edges just begin to soften.
Pour the white wine into the skillet to deglaze, simmering until the liquid has completely evaporated and coated the apples in a concentrated reduction.
Remove apples from heat and set aside.
Spread the remaining butter on one side of each sourdough slice.
On the non-buttered side of two slices, spread 1 tablespoon each of cranberry sauce.
Layer half of the brie slices, the wine-reduced apples, and fresh thyme onto the cranberry-coated bread.
Top with the remaining brie and the second slice of bread, buttered side facing out.
Place sandwiches in a cold non-stick skillet and turn heat to medium-low.
Grill for 4-5 minutes per side, pressing gently, until the sourdough is deeply golden and the brie has reached a fluid state.