Preheat the oven to 200C/400F/Gas 6.
For the millefeuille, place the puff pastry rectangles onto a non-stick baking sheet. Transfer to the oven and bake for 8-10 minutes, or until the pastry is risen and golden-brown. Remove from the oven and allow to cool.
Place the egg whites into a large clean bowl and whisk until stiff peaks form when the whisk is removed. Gradually add the sugar, whisking continuously until the mixture is thick and glossy. Gently fold in the pecans and melted chocolate.
For the vanilla cream, place the whipped cream into a bowl, add the vanilla seeds and gently stir.
For the coulis, place the icing sugar and berries into a food processor and blend until smooth. Strain the mixture through a sieve to remove the pips.
To serve, place one piece of pastry onto a serving plate and top with half of the pecan and chocolate mixture. Top with another piece of pastry, followed by the remaining pecan and chocolate mixture. Top with the final piece of pastry. Garnish with dollops of vanilla cream and drizzle over the coulis.