Cut pastry sheets into four squares each, and slice brie into eight pieces. Place brie and apple in center of pastry square. Sprinkle with cinnamon sugar.
Whisk egg and water together and use mixture to fold and seal corners into center of pastry. Brush top with additional egg mixture.
Arrange pastries on a lined baking sheet. Bake for 20 minutes.
Recipe by Rachel Schultz at https://rachelschultz.com/2018/02/05/apple-brie-pastries/