Pour the milk into a saucepan and bring to the boil.
Meanwhile, combine the egg yolks, cornflour and sugar in a heatproof bowl and whisk until smooth.
Remove the hot milk from the heat and slowly pour the milk onto the egg yolk mixture in a steady stream, whisking constantly.
Return the mixture to the pan and cook over a low heat, stirring constantly with a wooden spoon until thickened. (You should be able to draw a line through the custard on the back of the spoon using your finger: if the line is well-defined, the custard is ready.)
Remove from the heat and strain into a jug. Flavour with a few drops of vanilla essence, if you like, and serve hot.
Note: if you will not be serving the custard immediately, strain the custard into a bowl set over an ice bath to cool. Refrigerate before using, or up to three days.
Vanilla adds a lovely flavour to custard but you can add other flavourings such as a little grated orange zest or 2 tablespoons of brandy, rum or liqueur to the custard.
So much nicer to do it this way rather than using custard powder. Beware: do not let the mixture come to a simmer at step 4 or it will have a slightly lumpy 'scrambled' appearance - disaster!! - 22 Feb 2010