I need to explain a few things with this recipe. First of Ratafia is a type of liqueur or cordial flavoured with lemon peel, herbs in various amounts (nutmeg, cinnamon,clove, mint, rosemary, anise, etc.). Thanks Wikipedia.
It is a classic recipe that appeared even in a 1789 cookery book entitled Cookery and Pastry by Mrs MacIver that you can access on Google books. I have embedded the book below so you can see what other fantastic recipes exist. It even has a search function! This little drink would make excellent party appetisers or even a pudding course, depending on how thickly it turns out.
But this seems to be the non-alcoholic version. By 1851 it had morphed into a concoction using Brandy and Ratafia, but if you don't have Ratafia to hand, then a good malt whiskey should do nicely.
The recipe calls for heating the mixture over boiling water, so in a similiar way that you would make a chocolate sauce with a bowl in a large saucepan.
1. Gradually stir two glasses of Brandy in to a quart of cream. Heat over boiling water stirring constantly, until hot but not boiling.
2. Then gradually stir into 4 or 5 well-beaten egg yolks. Return to the top of double-boiler and stir over hot water until thickened but do not allow to boil.
3. Flavour the taste with Ratafia or Noyeau (generic word for liqueur). Add the strained juice of a lemon or a Seville orange can be stirred in as well before reheating.
Serve in glasses after chilling.