Mix flour, salt, and 200ml water into a dough and chill for 1-2 hours.
Roll pastry to 50x30cm, top two-thirds with sliced butter, and fold to enclose the butter.
Fold pastry into thirds, roll to 60x25cm, and fold into thirds again.
Perform two more single turns and chill for 30 minutes.
Roll pastry to 8mm thick, cut into two 28x10cm rectangles, and dust with icing sugar.
Bake at 200°C for 15 minutes until golden and let cool.
Warm milk with split vanilla pods over low heat.
Whisk yolks and cornflour, temper with warm milk, and cook until thickened.
Whisk cream with vanilla seeds and sugar until stiff, then fold into the custard.
Blend raspberries and lemon juice, sweeten with sugar, and strain through a sieve.
Layer split pastry pieces with cream and raspberries, finish with icing sugar, and serve with sauce.