Stir in sage and nutmeg and season with salt and and pepper to taste.
Add brandy if using.
Sprinkle flour over mixture and mix well.
Whisk in apple juice, reduce heat and simmer until thickened.
Add chicken and mix to combine. Simmer for 2 minutes.
Remove from heat and set aside to cool completely.
Assembly
Roll pastry if required.
Using pizza cutter or a sharp knife, cut into six 5-inch (12.5 cm) squares. Repeat with remaining dough.
Brush edges of squares with egg wash.
Place about ¼ cup chicken mixture in center of each square and top with 1 slice of Brie.
Either fold squares in half diagonally, enclosing filling or use two pieces of puff pastry. Pinch together edges to seal, and crimp with the tines of a fork.
Brush tops with egg wash.
Place pies, on parchment-lined baking sheets, in freezer for 30 minutes.
Position oven racks in upper and lower thirds of oven and heat oven to 375F/190C.
Bake for 25 minutes, switching positions of baking sheets halfway through, until puffed and deep golden brown.
Let pies cool on sheets on wire racks for 5 minutes before serving. Filling will be very hot.
Recipe by Orgasmic Chef at https://orgasmicchef.com/chicken-and-brie-puff-pastry-parcels/