Beat egg yolks, cornflour and sugar in a bowl until smooth.
Make sure the stirrer attachment is in place in the HomeCooker pan; set the temperature to 175°C. Bring the milk to the boil, 5 minutes.
Slowly pour the milk into the egg mixture, stirring constantly.
Return the mixture to the pan of the HomeCooker and set the temperature to 110°C for 10 minutes, so that the sauce thickens to a custard consistency. Flavour with a few drops of vanilla extract. Remove from the heat and strain into a storage container.
You can add other flavourings such as rum, brandy, flavoured liqueur or citrus zest.