For the pastry
350g/12oz plain flour
50g/2oz caster sugar
250g/9oz butter, diced
For the filling
3 cooking apples, about 600g/1lb 6oz
3 pears, about 500g/1lb 2oz
2tbsp lemon juice
450g/1lb ripe plums, stoned and quartered
75g/3oz caster sugar
beaten egg, to glaze
extra sugar, for sprinkling
Preheat oven to 190°C/375°F/Gas Mark 5.
Put flour and sugar into a bowl. Add butter and rub in with fingertips or an electric mixer. Press into a dough with hands. Wrap in cling film and chill for 30min.
Quarter, core, peel and slice apples and pears, toss in lemon juice. Put into a bowl with the plums, sugar and cornflour and toss together.
Knead pastry and roll out on a well-floured surface to form a 35.5/14in circle.
Lift over a rolling pin and drape in a 23cm/9in springform tin. Fill with fruit mixture, fold pastry around top edge of pie tin, repairing any breaks in the pastry. Brush with egg and sprinkle with sugar.
Bake for 35-40min until golden, covering with foil after 20min if going too brown.
Serve warm with custard.