Grate the white chocolate into a bowl and set aside. Pour the cream and vanilla bean paste into a saucepan over medium heat and heat until it just comes to a boil. Remove from the heat and allow to cool for about 30 seconds then pour over the grated chocolate. Stir with a whisk until the mixture is smooth. Cover with plastic wrap so that the wrap is touching the top of the cream. Once it has cooled sufficiently, refrigerate it until cold, preferrably overnight.
Cut your puff pastry into 12 equally sized pieces. We cut ours to 4.5 by 12 cm. Place on a tray lined with baking paper. Generously dust with powdered sugar, using the fine-mesh sieve to remove any bumps. Place another piece of baking paper on top and then top with the second baking sheet so that the tray is sitting against the pastry with only the baking paper between them.
Preheat the oven to 180°c. Bake the pastry on the middle rack of the oven for 20 minutes or until teh pastry is cooked and browned and the top is lightly caramelised. Remove from the oven and allow the pastry to cool on a wire rack.
Remove the cream from the refrigerator and beat on high for 2-3 minutes until soft peaks form. Add the mascarpone and beat until well combined.
Wash the fruit and set aside some for the top. Cut and slice the rest of the fruit into pieces that have the same thickness.
Assemble each mille-feuille: Pipe a layer of cream onto one pastry wafer. Top with pieces of fruit and a little more cream to stick the next layer of pastry on top. Repeat. Pipe the top layer of cream - a little more artfully if you like - and place the reserved berries on top. Enjoy!
Notes
If you are using white chocolate pieces and cannot grate them, melt the chocolate using your preferred method before adding the hot cream and vanilla.