Melt butter in a large frying pan over medium heat. Cook apple, stirring occasionally, for 4-5 minutes until tender. Stir in maple syrup, sugar, and cinnamon. Cook, stirring, for 4-5 minutes until liquid boils and thickens.
Transfer mixture to a bowl. Stir in sultanas. Set aside for 15 minutes to cool, then chill until mixture is cold. Preheat oven to hot, 200°C Cut each pastry sheet into 4 even sized squares.
Spoon 2 tablespoons of apple mixture onto one half of each pastry square. Brush edges with a little egg. Fold pastry over filling to form a triangle, pressing edges to seal. Brush with remaining egg. Bake for 15-20 minutes until golden. Dust with icing sugar and serve with icecream.