Preheat your oven to 180C Fan / 200C / Gas 6
Remove your bought Puff-Pastry from the fridge and unroll, place this on baking paper on a baking tray (now so you don't have to transfer it once you've made it)
Next quickly peel and core your apples. Chop into 1 cm dice or a little larger if you like firmer pieces of apple
Add your soft brown sugar, cinnamon & sultanas and give it a good stir
Now using a spoon place your apple mixture down the centre of the pastry (taking up the middle third - see pic)
Then place one side of the pastry half over the top and brush with beaten egg
Next place the other third of the pastry over the top - forming a big long parcel
Press down and make sure the pastry is attached to the other pastry and seal the edges at each end. Score lines across the top - it looks pretty!
Brush the whole strudel in beaten egg and sprinkle you white caster sugar over the strudel
Bake in the centre of your preheated oven for 40 minutes. After about 25 minutes check the top of your strudel, if it's browning to quickly pop a piece of baking paper over the top to stop it burn ing
After 40 minute your strudel will be baked and crispy on the top and bottom
Leave to cool for a little while - the filling is so so hot (be careful)
Dust with icing sugar and serve