Make the pastry. Add the flour, salt and butter to a bowl, then rub the butter in with your fingertips or an electric mixer until you have fine crumbs. Add the egg and water and continue mixing until the pastry just starts to come together. Transfer to a lightly floured surface, knead gently. Wrap the dough in clingfilm and chill for 30 minutes.
Roll out the dough thinly on a lightly floured surface and use it to line a 23 cm (9 inch) square flan tin (see
Cream the butter and sugar until pale and light, then gradually beat in the eggs, adding the flour and salt as you go until evenly combined. Stir in the syrup (the mixture may appear to curdle at this stage), nuts and chocolate and spoon the mixture into the pastry case.
Bake for 40–45 minutes until golden and just firm in the centre. Remove from the oven and leave to cool. Serve warm with ice cream.