Prepare a large bowl of ice and place a medium-sized bowl on top - this is to cool down the custard base once cooked.
Put the milk, cream, vanilla seeds, egg yolks and sugar in a bowl and whisk to combine. Pour the mixture into a heavy-based saucepan over low heat and add the vanilla bean. Stir continuously with a spatula or spoon and cook to 82°C (180°F); use