Scrape the vanilla bean seeds into the milk in a heavy-based saucepan. Add the vanilla bean and heat until the milk is hot but not boiling. Leave to infuse for 5-10 minutes. In a bowl mix together the egg yolks and sugar, then add the infused milk, stirring constantly. Wipe out the saucepan and return the mixture. Cook over a low to moderate heat, stirring constantly until the custard thickens enough to lightly coat the wooden spoon. Pour custard into a clean bowl, sprinkle with vanilla sugar to prevent a skin forming. Leave to cool, then cover and refrigerate. Remove vanilla bean before serving. Serve vanilla custard in glasses or pour into a jug and serve with poached fruit.