Blackberry millefeuille

Method

1. First, make the custard. Put the milk and vanilla in a small pan and heat gently. Put the egg yolks and sugar in a medium bowl and whisk until combined and slightly lighter in colour, then whisk in the cornflour. As soon as the milk starts to steam and quiver (but isn’t quite boiling), remove from the heat and gradually pour it over the egg mixture while whisking constantly. Once it’s all combined, tip the mixture back into the pan and put over a medium heat. Cook for about 5 minutes, stirring constantly but slowly with a rubber spatula until very thick. Scrape into a bowl and cover the surface directly with a piece of baking paper. Set aside to cool, then chill in the fridge.
2. For the coulis, put the blackberries, icing sugar and a splash of water in a small pan over a medium heat. Simmer until the berries have completely broken down (about 5 minutes). Taste the mixture; if the berries are quite tart you may want to add a bit more sugar. Spoon into a blender, then whizz to a smooth purée. Tip into a bowl, leave to cool, then chill until needed.
3. Heat the oven to 200°C fan/gas 7. Cut the block of pastry in half and roll out each piece into a rectangle measuring 21cm x 27cm. Transfer each rectangle of pastry to a baking tray, then sit another baking tray on top (this will stop it puffing up too much as it cooks). Bake for 20-25 minutes until a deep golden brown; you want the pastry to be dark and well caramelised rather than pale and light. Set one tray aside to cool, then use a fine sieve to dust the second pastry sheet with the icing sugar. Return the sugar-dusted pastry to the oven (without a tray on top) for 3-5 minutes until the sugar has dissolved and caramelised, giving the pastry a shiny surface. Set aside to cool completely.
4. Whisk the cream to soft peaks, then fold it through the chilled custard with a large metal spoon using a figure-of-eight motion. Transfer to a piping bag. Put the chilled coulis in another piping bag.
5. Use a large, sharp knife to cut each sheet of pastry into 9 even rectangles, around 7cm x 9cm. You’ll need 3 rectangles for each mille-feuille, reserve 6 of the sugar-coated ones for the tops. To assemble the mille-feuille, pipe 6 even blobs of the custard cream – in 2 rows of 3 – on each of 6 rectangles, leaving space for a blackberry between each blob. Pipe a dot of blackberry coulis into the gaps, then sit the blackberries on top. Pipe a little more blackberry coulis on top, then sit another pastry rectangle on top and repeat. Top with a reserved sugar-coated pastry rectangle. Once assembled sift over some more icing sugar and serve immediately.