Put the milk, sugar and vanilla pod in a pan with a pinch of salt and bring just to the boil. Leave to cool. Swish the vanilla pod around to release the seeds then pull it out (rinse and dry and stick it in your sugar jar) and reheat the milk. Beat the egg yolks together and whisk them thoroughly into the milk. Put the pan back over a low heat and stir until the custard is thick enough to coat the back of the spoon. Keep stirring and don’t let it overheat or you’ll end up with scrambled eggs. The whole process should take around 8-10 minutes.