Step 1
To make the custard, put the cream, milk and vanilla seeds into a saucepan and heat to just below boiling. In a bowl, whisk together the sugar, egg yolks, and cornflour. Still whisking, pour in the hot milk mixture. Return to the pan and heat gently, stirring until the mixture begins to thicken and coats the back of a spoon. Pour into a bowl. Stir in the butter. Place a sheet of clingfilm directly onto the surface of the custard. Put in the fridge and chill until completely cold.