Preheat the oven to 200°C. Use a sharp knife to cut the pastry sheet into twelve rectangles, each one measuring 5 x 10 cm. To do this, cut two strips that are 10 cm wide, 25 cm long. Cut the remaining thin strip into two lengths that are 10 cm long. Now take the two large strips and cut each one across the width into five equal pieces – these should measure 5 x 10 cm. Arrange on a slightly damp baking tray and place a wire rack on top, so they rise evenly during baking. Bake for 10 minutes until puffed and golden.
Remove the wire rack, sprinkle the pastry with half of the icing sugar and bake for a further 5–10 minutes until the sugar has caramelised. Cool on a wire rack.
Whip the cream, then lightly fold in the remaining icing sugar and the vanilla essence.
Just before serving, spoon or pipe half the cream in a layer onto four pastry rectangles and cover with one third of the kiwi slices. Top each one with another pastry rectangle, the remaining cream and more kiwi slices, to make a second layer. Place the last four pastry rectangles on top, finishing with the remaining slices of kiwifruit. Dust with icing sugar, decorate with sprigs of mint and serve.