This is what the French call creme anglaise. Once you know how to make real custard, powdered packet custard is a poor substitute.
- Put the cornflour and egg yolks into a heatproof bowl and beat well so there are no lumps. Reserve.
- Put the milk, vanilla and sugar into a saucepan and gently bring to the boil.
- Remove from the heat and gradually add the hot milk mixture to the egg yolk mixture, beating continuously.
- Place over a saucepan of barely simmering water and stir until the mixture coats the back of a spoon. Don’t let it get too hot or it will curdle. (If it does curdle, pour into a blender or use a wand mixer and blend until smooth. It will be runnier than it should be but will still taste good.)
See Ray's winter puddings