In a bowl, add the egg yolks and lightly beat. Then slowly pour in half of the milk mixture, stirring as you pour. Return the bowl mixture to the saucepan and bring to a gentle boil, stirring all the time then add the remaining milk mixture until it starts to boil. At this point, have a little taste to see if you have the amount of sweetness to your liking. If you need more, simply add a tablespoon of sugar at a time and taste as you go along. Remove from heat, add the vanilla extract, stir, then serve or transfer to a bowl to cool if desired.