Put the apples, plums, caster sugar, flour and cinnamon in a wide pan. Soften the fruit for about 5 minutes, until they start to turn saucy but not completely soft. Take off the heat, stir in the sloe gin and leave to cool.
When the fruit is cool, preheat the oven to 190°C (170°C fan oven) Gas Mark 5. Spoon the fruit filling into a deep, roughly 20cm pie dish. Brush the edges with a little egg white.
On a lightly floured surface roll the pastry out to a round, ½cm thick. Lift onto the pie, press down to stick at the edges and trim the excess. Use the excess to make decorations, if you like, and stick on with more egg white.
Use a pastry brush to lift off the egg white froth and brush the pie with this bubbly mixture. Sprinkle over the granulated sugar and bake for 40-45 minutes until the pastry is dark golden and crisp. It’s best served with custard.