In a large saucepan, boil the milk with the vanilla paste.
Whisk the egg yolks with sugar and add the cornflour, pour the warm milk into the egg mixture, a little at a time whilst whisking.
Place the saucepan back on a medium heat. Cook to a boiling point, until thickened like a bechamel texture, stirring constantly for 3-5 minutes.
Pour the crème Patissière into a bowl and lay a layer of cling film over the mixture to prevent a skin forming.
Allow to cool in the fridge for 20-30 minutes. Use as needed within 2 days.