In a large bowl, mix together the flour, lemon rind and salt. Cut 60g/2½oz butter into pieces. Rub into the flour mixture with your fingertips to form coarse crumbs. Stir in sugar. Put mixture in the freezer for 20 minutes.
Meanwhile, peel, core and chop the apples. Melt the remaining butter in a pan. Add the apples and cook, stirring regularly, for 10 minutes.
Cover and cook for 5-10 minutes, or until tender. Add the golden syrup. Increase the heat and cook until the apples start to caramelize.
Transfer the apples to a plate and keep warm. Wipe the pan clean. Set pan over a medium heat. Add crumble. Cook for 5 minutes, without stirring, until golden. Spoon the apples into 4 bowls and top with crumble. Serve.