About this recipe:French Vanilla Slices are called 'Mille-feuilles' and are made with puff pastry sandwiched together with jam, cream or custard. They can be dusted with icing sugar or iced. Make sure you allow time for the pastry to cool before assembling.
In a small saucepan, heat milk until small bubbles form. Drop in the vanilla pod (or add essence) remove saucepan from heat, and set aside to cool until just warm.
In a medium saucepan, stir together the flour, sugar, salt, and egg yolks. Beat for a moment, then gradually whisk in warm milk. Simmer over medium-low heat until the custard thickens, stirring constantly with a wooden spoon to prevent sticking.
Transfer custard to a bowl, and allow to cool, stirring from time to time.
Preheat oven to 200C. Roll out the puff pastry into a single sheet about 1 cm thick; it should be the same size as a 43x53cm baking tray. Place the pastry onto the baking tray and prick all over with a fork.
Bake in preheated oven until cooked,about 20 minutes. Remove from oven, and cool pastry on the baking tray.
When the pastry has cooled completely, transfer it to a hard surface and cut lengthwise into three 10 to 12 cm wide strips.
Spread one strip thickly with custard. Place a second strip directly over the first; spread the top evenly with jam. Cover with the third strip, and dust with icing sugar. With a very sharp knife, cut into 8 rectangular portions.