Preheat the oven to 200C/400F/Gas 6.
For the millefeuille, using a sharp knife cut two 13 x 7cm/5 x 3in rectangles from the pastry and lightly score the surfaces. Glaze the pastries with the beaten egg, using a pastry brush. Sprinkle the cinnamon and brown sugar over the top.
Place the pastry onto a baking sheet lined with greaseproof paper and bake for about 8-10 minutes, or until lightly golden-brown and crisp.
For the vanilla cream, lightly whip the double cream until soft peaks form. Slice the vanilla pod in half lengthways, then remove the seeds and fold into the cream.
For the strawberry coulis, blend 100g/3½oz of the strawberries and the icing sugar in a small food processor until smooth. Pour half of the mixture into a bowl and set the other half aside. Cut the remaining strawberries into quarters and fold into the coulis in the bowl along with the chopped fresh mint.
To serve, spoon a little of the vanilla cream onto the middle of a serving plate. Place one piece of pastry on top followed by half of the cream. Arrange half of the strawberries on the cream, then top with the second pastry rectangle, the remaining cream and remaining strawberries. Spoon the reserved strawberry coulis around the millefeuille and garnish with a sprig of mint.