In a large saucepan heat the butter over medium heat until it begins to foam. Add the apples and half the sugar and cook for ten minutes, stirring often. You are trying to cook off excess water from the apples. Remove the apples from the heat and tip them into a colander to drain any excess liquid for a few minutes. Transfer the apples to a mixing bowl and add the rest of the sugar, golden syrup and the cinnamon powder. Place the mix into the fridge while you prepare the pie tin.
Butter a 20cm pie tin and place one sheet of the pasty onto the bottom, leaving the edges hanging over. Spoon the cool apple mix into the pie tin and top with the other sheet of pastry. Crimp the edges to seal and cut around the outside of the pie tin to create a uniform crust. Brush the top with eggwash and dust in raw sugar, place a slit in the top of the pastry and bake for 30-35 minutes or until pastry is golden brown and crunchy.