Caramelise the apples: Mix the sugar, cinnamon and nutmeg, then toss the apple chunks to coat. Melt half the butter in a wide pan and fry half the apples over high heat until golden at the edges, about 5 minutes. Repeat with the rest, then leave to cool completely.
Line the tin: Roll half the pastry and line a 20cm metal pie tin, pressing out trapped air. Roll the rest for the lid.
Fill and seal: Spoon in the cooled apples. Brush the rim with water, lay the lid over, press to seal, crimp and trim.
Glaze and bake: Egg wash, sprinkle with sugar, cut a small cross in the top for steam. Bake at 190C on a preheated metal tray for 35 to 40 minutes until deep golden. Rest 15 to 20 minutes before slicing.
