Make the pastry cream by putting the milk, sugar, butter and vanilla in a medium saucepan and place on a medium heat.
Gently warm until the butter has melted, making sure the milk does not come to a boil.
In a second bowl, whisk the cornflour and egg yolks until smooth. Remove the milk from the heat, then very slowly pour it over the egg yolk mix, whisking continuously until very smooth.
Return the mixture to the pan, and cook on a medium heat for eight to 10 minutes, stirring continuously, until the custard bubbles and thickens. Stir in a pinch of salt, then pour the custard into a shallow, heat-proof dish. Cover with cling-film – you want the film actually to touch the surface of the custard, because this will prevent a skin forming – refrigerate for 30 minutes and then let it stand at room temperature to set.
Put all the ingredients for the macerated strawberries in a medium bowl, stir gently to combine, then refrigerate for at least an hour, but no longer than three hours.
Preheat the oven to 190°C. Cut out a 23 cm square from a puff pastry sheet and lay this on an oven tray lined with grease-proof paper.
Using the back of a knife, score a square inside the pastry to leave a 1.5 cm border around the edges (by using the back of a knife, you’ll make sure you don’t cut all the way through the pastry)
Brush the milk evenly all over the pastry, sprinkle evenly with the sugar, then bake for 20 minutes, until risen and golden brown and leave to cool.
To assemble :
Gently push down the central square of pastry to create a space for the cream, then spoon in the cream, smoothing the surface as you go. Strain the strawberries through a sieve over a medium bowl and arrange the strawberries on top of it, drizzle with a bit of the strained strawberry liquid, sprinkle over the pistachios, and serve.
Reprinted with permission of Heinstirred.