Wow-Wow Sauce is a sauce, apparently created by Dr. William Kitchiner in the early 19th century. It contains port, wine vinegar, pickled cucumbers or pickled walnuts, English mustard and mushroom ketchup in a base of beef stock, flour and butter. The original recipe appeared in the 88th edition of the 1894 edition of the book "Enquire Within Upon Everything." It is believed Kitchiner 'borrowed' the recipe from "The Cook's Oracle," first published in 1817.The recipe was revived in "Farmhouse Cookery, Recipes from the Country Kitchen" By Molly Harrison, Reader's Digest, 1980, 1982.

'Discworld' Wow Wow Sauce, a favourite of Mustrum Ridcullys, contains (as stated in Reaper Man):
Matured Scumble (which contains apples, well mostly apples).
Pickled Cucumbers
Capers
Mustard
Mangoes
Figs
Grated Wahoonie
Anchovy Essence
Asafetida
A good deal of Sulfur and Saltpeter

Wow-Wow sauce is one of the ingredients in the "ultimate hangover cure" the Unseen University wizards create in Hogfather. The recipe can also be found in "Nanny Ogg's Cookbook" originally published 1999, in Great Britain by Doubleday, by Terry Pratchett and Stephen Briggs, with illustrations by Paul Kidby.