Put the milk in a saucepan. Cut the vanilla pod, if using, down one side, then scrape out all the seeds. Add the pod and seeds to the milk and place the pan over a medium heat. Scald, by gently heating until steaming. Just before it bubbles, take off the heat and remove the vanilla pod and any skin that has formed. Put the egg yolks and 1 tablespoon of the sugar in a medium bowl and stir to mix. Pour in a little of the scalded milk and stir, then add the remaining milk gradually, stirring continuously until fully combined. Rinse out the saucepan used to scald the milk. Return the milk and egg mixture to the cleaned pan. Place over a low to medium heat and stir continuously with a wooden spoon. First the custard will steam, which is an indication that it is about to thicken. Watch it carefully and keep stirring, getting the wooden spoon well into the corners. To test if the sauce is thickened, remove it from the heat and draw the back of the spoon through the sauce. It should coat the back of the spoon evenly and not drop away and pool at the base of the spoon. When you draw a clean finger down the back of the spoon through the custard the trail should remain. This indicates that the sauce is ready. When this point is reached, immediately strain the sauce through a chinois or fine sieve into a bowl. Taste and add more sugar if necessary. Set aside to cool. If you are using vanilla extract, add a few drops now. To prevent a skin forming, place a disc of greaseproof paper on the crème anglaise, in direct contact with the surface.