Preheat an oven to 400°F (200°C).
In a large skillet, melt the butter. Add the sliced apples, raisins, cranberries, walnuts, sugar, cinnamon, and nutmeg and cook for 5-7 minutes until the apples soften a little bit but are still firm. Let cool.
On a lightly floured surface, roll out the puff pastry sheet into 12x9 inch rectangle. Place it on a parchment paper lined sheet pan.
Spread the apple filling over the center of the pastry sheet creating a log. Cut slits 1 inch apart along the two sides of the sheet to within ½ inch of the filling.
Fold the strips over the filling, alternating left and right to create a braid. When it comes to the other end, fold the end and finish the final strips to secure. Brush the pastry with the beaten egg.
Bake for 15-20 minutes or until golden brown. Let it cool before slicing. Sprinkle with the powdered sugar and enjoy!