4 Hard Boiled Egg Yolks
4 tbsp Cream
1 tsp Prepared Mustard
¼ tsp White Pepper
Vinegar
Salt and Cayenne, to taste

Remove the egg shells, and pound the yolks in a mortar to a smooth paste.
Add the other ingredients, except the vinegar, stir well until thoroughly combined.
Pour in enough vinegar, a little at a time, to make it the consistency of cream.
The mixture will then be ready for use.

Thank you! I will try it this weekend - warm and sunny here for the first day in ages, so great for a BBQ and salad with genuine postgrad-forum salad cream.