Apple crumble cheesecake

Name: Apple crumble cheesecake
Ingredients: 100g/3½oz plain flour; 100g/3½oz light soft brown sugar; ½ tsp ground cinnamon; 50g/2oz unsalted butter; 1 tsp milk; 100g/3½oz butter; 250g/9oz oat biscuits, crushed; 1 large Bramley apple, peeled, core removed, sliced, mixed with 1 tbsp lemon juice; 500g/1lb 2oz mascarpone cheese; 400g/14oz cream cheese; 125g/4½oz caster sugar; 1 vanilla pod, split lengthways, seeds only; 1 x 150ml/5fl oz tub soured cream; 4 free-range eggs; 100g/3½oz sultanas (optional); ¼ tsp grated nutmeg