In a freestanding mixer, or using an electric hand mixer, whisk together the egg yolks and sugar until pale in colour.
Add the flour and cornflour then continue to whisk until fully blended.
In a saucepan, heat the milk and vanilla bean paste/pod together until it reaches a gentle simmer. Stir regularly and be careful not to boil at this stage. After a few minutes simmering remove from the heat.
Gradually pour the vanilla milk mixture into egg mixture, continually whisking at the same time. Then once all of the ingredients have combined transfer back into the saucepan.
Heat the saucepan, bringing the custard to a boil and stir for 1-2 minutes at a simmer, until it reaches a smooth consistency. Continual whisking will help prevent lumps from forming.
Remove from the heat and pour into a bowl to cool. To speed up the cooling process you can place the bowl inside a larger bowl containing ice cubes. Alternatively, pouring the mixture into a larger shallow container will help the mix cool quicker.
Once cool, cover with cling film to prevent a skin forming and chill in the fridge until you are ready to use.