250ml (1 cup) milk
1 vanilla bean, split
1/2 cup cornflour
3/4 cup custard powder
220g (1 cup) caster sugar
750ml (3 cups) thickened cream
50g unsalted butter
3 egg yolks
Icing sugar to dust
Preheat oven to 210°C. Line a 20cm square pan with aluminium foil, so that the foil comes up over the sides (this allows you to lift out the slice).
Place each pastry sheet on a baking tray lined with non-stick baking paper, then bake for 8-10 minutes or until golden brown. Set aside to cool. Once cool, place 1 pastry sheet, cooked-side up, in bottom of pan. (You may need to trim it slightly to fit.)
Place milk in a pan over medium heat. Scrape in vanilla seeds and add bean too. Warm gently, then set aside for 10 minutes.
Place cornflour, custard powder and caster sugar in a pan. Strain milk, discard bean*, into pan with cornflour and whisk until smooth. Add cream, then return to heat, stirring constantly, over low heat until the mixture thickens and boils. Add butter, stirring well to combine, then remove from heat and whisk in egg yolks, one at a time, until smooth. Pour into pastry-lined pan and set aside to cool slightly before placing other piece of pastry, cooked-side up, on top. Refrigerate overnight.
Remove from pan, dip a knife into hot water and cut the vanilla slice into squares, dust with icing sugar.
*I never throw my vanilla beans away, I simply rinse them under cold water, let them dry and then keep them in a screw top jar with sugar, it makes the most amazing vanilla sugar.