Gather all ingredients: sourdough bread, brie cheese, blackberries, balsamic reduction, and butter.
Spread 1 tablespoon of butter evenly on one side of each slice of sourdough bread.
Place one slice of bread on a board, buttered side down, and layer 2 ounces of brie cheese on the unbuttered side.
Arrange half of the blackberries on top of the brie, pressing gently.
Add fresh basil leaves on top of the blackberries if using.
Drizzle 1 tablespoon of balsamic reduction over the blackberries.
Top with the second slice of bread, unbuttered side facing the filling, and press down gently.
Heat a non-stick skillet over medium heat and place the sandwich in the skillet.
Cook for 3-4 minutes until golden brown, then flip and cook for another 3-4 minutes until the cheese melts.
Remove from skillet, let sit for a minute, then cut in half diagonally and serve.
Notes
This sandwich can be served as a standalone meal or as part of a brunch spread. Experiment with different types of bread or add complementary ingredients.