Fill a three quart saucepan with the five cups of milk and heat on medium on top of the stove. Lower the temperature just before the boiling point and keep warm until ready to use.
Break the three whole eggs and the five yolks in a bowl with the 1/2 cup sugar, the 1/8 tsp salt and the tsp of vanilla. Whisk until light and foamy.
Pour the hot milk over the egg mixture in a very thin stream while whisking constantly until all the milk is mixed with the eggs and it is foamy.
With a ladle, fill each container with the milk/egg mixture.
Also with a ladle, add the hot water to the pyrex dish(es) so that the water comes up to at least half of each ramequin.
Set in the oven and let it bake for 45 minutes to one hour.
When cool, circle a knife gently around the inside edge of the container, cover it with a plate and with a quick motion, reverse the ramequin so that the plate is under it. Wiggle to dislodge the custard or shake it gently with an upward/downward motion.