To make the filling: Cook apples in water and sugar in a heavy-based saucepan. Simmer until apples turn soft. Add cinnamon stick, lemon juice and butter and continue to cook until mixture reaches the right consistency (can sift in flour to thicken further). Dish out to cool. If you prefer a smooth filling, puree the cooked filling.
To make the pastry: Sift flour and salt into a mixing bowl, add sugar to combine. Add butter and, using your fingertips, quickly and lightly rub the butter until mixture resembles fine breadcrumbs.
Make a well in the centre of the flour mixture, stir in water and lemon juice and work together until a fairly stiff dough is formed. Try not to break up the pieces of fat or butter too much.
Form the pastry into a ball. If it is slightly sticky, add a little more flour. Wrap the pastry with cling film and chill in the refrigerator for at least 30 minutes before using.
To make the puffs: Cut the pastry in two. On a lightly floured surface roll out into a sheet of 2mm thickness. Cut out 10cm x 6cm rectangles. Spread about 1 1/4 to 2 tbsp of the apple filling on each rectangle. Damp the edges and close up with another piece of rectangle.
Press the edges together well to seal. Use a fork and press down on the edge of the pastry to form a decorative pattern. With the pointed edge of the knife make a small steam vent on top of each pastry.
Place puffs on trays lined with parchment paper and chill for 10 minutes. Glaze the puffs with beaten egg and bake in a preheated oven at 200 °c for 15 minutes or until they turn golden brown.