Grease six 4oz (1/2 cup) ramekins or jelly jars with butter. Put them all onto a pan and set aside. Preheat oven to 176°F/80°C, steam setting (100% humidity).
Pour the milk and cream into a small pan. Scrape the seeds from the vanilla pod, if using, and add the seeds and pod to the pan. Bring to a simmer over medium heat, then turn off the heat, cover and leave to infuse while you make the caramel.
1 cup milk, 1 cup cream, 1 vanilla bean
Put the sugar for the caramel in a deep saucepan and just barely cover it with water. Bring to a simmer over medium heat, then cook until it’s syrupy and turning a golden amber color. Quickly remove from heat and divide the caramel between the moulds. Swirl to evenly cover the bases and come a little way up the sides. Set aside.
2/3 cup superfine sugar
When the infused milk has cooled until it's just warm, remove the vanilla pod. Add the sugar and whisk to combine. Tip in the eggs and yolks and whisk thoroughly, then pour the mixture through a sieve into a jug. Leave the mixture to settle for 15 minutes, then skim any foam from the top of the bowl.
2 eggs, 4 egg yolks, ½ cup superfine sugar
Pour the custard into the caramel-coated jars, dividing it evenly.
Cook the cremes for 1 hour, then remove from the oven. Cool to room temperature on the bench, then refrigerate overnight. The cremes need this overnight chilling and setting time so the caramel can soften into a liquid sauce.
To unmould, run a slim knife around the inside of each jar and invert on to plates, letting the liquid caramel run over the custard.