Line a large baking tray with greaseproof paper. Dust the work surface with lots of icing sugar and roll out the pastry to a rectangle just larger than 27 x 30cm/10Â½ x 12in, trimming the edges straight. It should be super thin, as thin as you can get it, without stretching the pastry.
Cut out 18 rectangles about 9cm/3Â½in long and 5cm/2in wide and place them on the prepared baking tray. Sprinkle with lots of icing sugar and put in the fridge for 30 minutes.
Preheat the oven to 200C/400F/Gas 6.
Remove the pastry from the fridge and bake in the oven for five minutes, then remove from the oven and sprinkle the pastry with more icing sugar. Return to the oven and bake for a further five minutes, or until the pastry turns golden-brown. Remove from the oven and set aside.
For the sweetened cream, put the cream, icing sugar and vanilla in a large bowl and whip until medium-stiff peaks form when the whisk is removed from the bowl. Fold in the lemon zest and juice, to taste, then scoop the mixture into a piping bag fitted with a 1cm/Â½in straight nozzle.
Place one of the pastry thins on a serving plate. Pipe blobs of cream over the pastry and put the blueberries between the cream, then put another pastry thin on top and repeat with one more layer. Sprinkle the top layer with more icing sugar and repeat until all the pastry and cream is used up.