Even though espagnole is the French word for Spanish, the sauce has little connection with Spanish cuisine. According to Louis Diat, the creator of vichyssoise and the author of the classic Gourmet's Basic French Cookbook:
"There is a story that explains why the most important basic brown sauce in French cuisine is called sauce espagnole, or Spanish sauce. According to the story, the Spanish cooks of Louis XIII's bride, Anne, helped to prepare their wedding feast, and insisted upon improving the rich brown sauce of France with Spanish tomatoes. This new sauce was an instant success, and was gratefully named in honor of its creators.
However, in Kettner's Book of the Table published in 1877, there is an entirely different explanation:
When the Bourbons made their way to the Spanish throne under Louis XV, and when Spanish fashions came back to Paris, the French cooks took a hint from the Spanish pot-au-feu — the olla podrida — and produced a variation of their brown sauce which they called Spanish. The essential principle of the French pot-au-feu was beef ; the essential principle of the Spanish was bacon, ham, the red Estremadura sausage — all well smoked ... The Duc de St. Simon sent home marvellous accounts of the hams of Montanches; there grew up a rage for Spanish hams; and the French were not to blame, for they have no hams of their own which have any reputation. Great as they are in pig's flesh, they are poor hands at bacon and ham; and the treasures of Montanches were a revelation to them. They ran wild after ham ... And so, by introducing the flavour of the Estremadura bacon and ham into the old brown sauce of the French, there came into being the Spanish sauce ... The hams of Montanches are not too plentiful in this world of sorrow, and the cooks came to be satisfied with any ham — even with French ham, which is little better than salted pork. So the meaning of the prescription was lost; the peculiarity of the Spanish sauce passed away, and its name became a puzzle.
(The name Kettner in the title refers to Auguste Kettner, former chef to Napoleon III who immigrated to England and in 1867 opened a restaurant in Soho– Kettner's– one of the oldest restaurants in London.)
The basic method of making espagnole is to prepare a very dark brown roux, to which are added several liters of veal stock or water, along with 10–15 kg (20–30 lb) of browned bones, pieces of beef, many pounds of vegetables, and various seasonings. This blend is allowed to slowly reduce while being frequently skimmed. The classical recipe calls for additional veal stock to be added as the liquid gradually reduces but today water is generally used instead. Tomato sauce is added towards the end of the process, and the sauce is further reduced.
Espagnole has a strong taste and is rarely used directly on food. As a mother sauce, however, it serves as the starting point for many derivative sauces, such as Sauce Africaine, Sauce Bigarade, Sauce Bourguignonne, Sauce aux Champignons, Sauce Charcutière, Sauce Chasseur, Sauce Chevreuil and Demi-glace. There are hundreds of other derivatives in the classical French repertoire.
A typical espagnole recipe takes many hours or even several days to make, and produces four to five quarts of sauce. In most derivative recipes, however, one cup of espagnole is more than enough, so that the basic recipe will yield enough sauce for 16 to 20 meals. Frozen in small quantities, espagnole will keep practically indefinitely.