In a large bowl, whisk the egg yolks and sugar until thick and pale. Bring the milk to the boil in a medium sized, heavy based pan with the vanilla bean and seeds. Remove the milk from the heat as soon as it comes to the boil and pour it over the egg/sugar mixture, whisking all the time. Pour this mixture back into the pot and cook, stirring all the time, until the mixture thickens slightly and coats the back of the spoon. Strain the mixture through a fine sieve and cool rapidly over an ice bath. When it’s cool, add the chilled cream and the vanilla extract. Refrigerate this mixture for a couple of hours (or, even better, overnight), then churn in the ice cream machine. When churned, transfer to a pre-chilled tub and place in the freezer to firm up to your desired consistency. I like to remove the ice cream to the fridge 30 minutes or so before serving to allow it to soften slightly.