Preheat the oven to 200°C.
Simmer chopped apples and water in a lidded pan for 4 minutes until soft.
Whisk the cooked apples into a smooth purée and allow to cool.
Roll the pastry into a 30cm circle and score a 1cm border inside the edge.
Brush the pastry twice with beaten egg yolk, waiting one minute between coatings.
Spread the cold apple purée over the inner circle of the pastry.
Arrange the apple slices in layers over the purée.
Brush apples with melted butter and sprinkle with caster sugar.
Bake for 30 minutes until the pastry is golden and apples are caramelised.
Serve slices with ice cream and a dusting of icing sugar.