For the pastry, mix the butter and sugar together until fluffy; add salt, lemon zest, bourbon vanilla and flour and quickly knead to a consistent dough.
Form the dough into a square shape, wrap in cling film and leave to cool in the fridge for 2 hours.
For the filling, wash the apples, peel and quarter them and remove the core.
Slice the apples in to approx. 2mm thick pieces and pour on lemon juice.
Mix the spices and sultanas together well. Remove the short crust pastry from the fridge and roll out to a square measuring 25 x 35 cm and around 3 mm thick. Place the filling in the middle of the pastry square, tuck over the left and right-hand edges and fold the pastry together. Brush with whisked egg and place on a baking sheet covered with grease-proof paper.
Bake for a short time in a preheated oven at 200º C, reduce the temperature to 190º C and then leave the strudel to bake for a further 35 minutes or so.
The short crust pastry will keep for up to 6 days in the fridge.