Cream 25 g (1 oz) of the butter with the sugar and almond essence or orange flower water until light and pale. Add the egg yolk and ground almonds, mix until smooth, then stir in the pistachios. Chill for 15 minutes.
Cut each apricot in half, remove the stones, then sandwich the apricots back together with the pistachio mixture in the middle.
Melt the remaining butter. Unfold the pastry sheets and put one sheet on your work surface. Brush with melted butter, then cut into 4 rectangles. Put an apricot on one of the rectangles, lift up the corners of the pastry to enclose the apricot, then pinch together at the top of the fruit. Wrap with a second pastry rectangle at right angles to the first to form a purse shape. Repeat with a second apricot and 2 more pastry rectangles, then place on a baking sheet. Continue until all apricots have been used.
Brush with a little of the remaining butter, then bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 15 minutes until golden. Dust with icing sugar and serve warm or cold with scoops of vanilla ice cream.