Bring the pastry sheet to room temperature and then slightly flatten using a rolling pin to make a sheet with uniform thickness. Prepare egg wash, by adding and mixing little bit of water to 1 egg. Preheat oven to 375 degrees F. Apply egg wash on top of the pastry sheet.Mix walnuts, brown sugar, white sugar and bread crumbs and add this mixture on the pastry sheet evenly. Mix together apple ,cinnamon, flour and sugar and put it on top of sugar filling. Keep the filling on the bottom of the sheet only. Fold the pastry sheet from both sides, pinch in the sides a bit to keep it all together.Make a long cut on top, about every 1/2 inch apart. Bake it for 40-45 minutes until golden brown.