1. Roll out the pastry to a thickness of about 5mm/¼in. Line a 25cm/10in tart tin with the pastry and bake blind.
2. Meanwhile, peel and core the apples, slicing the 'dissolving cookers' and chopping the 'hard eaters' into neat 1cm/½in dice. Put both kinds together into a saucepan with the lemon juice and 100g/3½oz of the sugar. Heat very gently until the juices begin to run. Cook the fruit, stirring occasionally at a very gentle simmer for 10-15 minutes, until you have a juicy compote of puréed Bramleys (or similar) with tender pieces of Cox (or similar).
3. To make the crumble: sift the flour into a bowl and rub in the butter until you have fine crumbs, then toss with the hazelnuts and sugar.
4. Spread the fruit into the cooked pastry case and sprinkle over the crumble in an even layer. Bake in a pre-heated fairly hot oven (200C/400F/Gas 6) for about 30 minutes, until the crumble top is nicely browned.
5. Serve the pie warm with vanilla ice cream or cream.
500g/1lb2oz sweet shortcrust pastry
1kg/2¼lb cooking apples such as Bramley
500g/1lb2oz hard eating apples, such as Cox's or James Grieve
juice of half a lemon
For the crumble:
100g/3½oz plain flour
75g/3oz unsalted butter
50g/2oz light brown or caster sugar
50g/2oz ground hazelnuts (or almonds)