step 1
Whisk the sugar, egg yolks and cornflour together in a bowl until smoothly combined and set aside.
step 2
Pour the milk into a large heavy based pan. Split the vanilla pods open (If using vanilla pods) and scrape out the seeds with the tip of a knife and add these to the milk in the pan. (Alternatively add the vanilla extract to the milk) Bring to the boil, then remove from the heat.
step 3
Pour about a quarter of the hot milk onto the egg mixture and whisk together. Then return this mixture to the rest of the milk in the pan. Put back over a gentle heat and cook, stirring continuously, until the mixture becomes thick. Remove from the heat immediately.
step 4
Pass the mixture through a sieve into a bowl. Add the butter and stir in to melt. Place a disc of baking parchment or silicone paper directly on the surface of the creme patissiere to stop a skin forming. Leave to cool and then chill before using.