1) Preheat the oven to 200°C/gas mark 6.
2) Combine the orange zest and orange juice in a bowl. Peel, quarter, and core the apples and then cut them in 2cm dice. Immediately toss the apples with the zest and juice to prevent them from turning brown. Add the cherries, sugar, flour, cinnamon, nutmeg, and salt.
3) Flour a board and lightly roll each sheet of puff pastry to a 30 x 30cm square. Cut each sheet into 4 smaller squares and keep chilled until ready to use.
4) Brush the edges of each square with the egg wash and neatly place about 1/8 of the apple mixture on half of the square. Fold the pastry diagonally over the apple mixture and seal by pressing the edges with a fork. Transfer to a sheet pan lined with parchment paper. Brush the top with egg wash, sprinkle with granulated sugar, make 2 small slits, and bake for 20 mins, until browned and puffed. Serve warm or at room temperature.