Make the filling by placing the cherries, water, sugar and cornflour in a saucepan. Stir until cornflour has dissolved, then place over a medium heat and cook until the mixture boils and thickens (this will take up to 5 minutes). Remove to cool.

Roll out two-thirds of the pastry to 3mm thick and use to line the base and sides of a pie dish. Prick the base all over with a fork and fill with the cold cherry mixture.

Roll out remaining pastry into a circle the same size as the dish and use to cover the cherry filling. Use the tines of a fork to seal the pastry edges and cut four small slits in the top of the pie to allow steam to escape during cooking.

Refrigerate for 20 minutes to chill. Meanwhile, heat oven to 180°C fan bake. Brush the surface of the pie with beaten egg. Bake for 45 minutes or until pastry is golden brown. Serve warm.