You may as well go the whole hog and use a vanilla pod. Otherwise, use vanilla sugar and/or stir in 1 teaspoon of good vanilla extract at the end. Or you can add 1 tablespoon of rum to the cream when heating it at the beginning.
It is helpful to know, when making custard, that you need 1 egg yolk for each 100 ml of milk or cream. It’s harder to be precise about the sugar, since that rea