Espagnole Sauce is a rich and delicate brown sauce and one of the five mother sauces of French cuisine. The fact that this sauce also known by the name Spanish Sauce is pointing to its origins in Spain, it is attributed to French chefs.
The five mother sauces are those coined by Auguste Escoffier as elemental sauces used as bases for several other variants. The other four sauces include Sauce tomate, Bèchamel sauce, Bearnaise sauce, and Veloutè sauce.
Espagnole sauce is a rich dark brown sauce originally made from veal stock or later beef stock or water and a brown roux. Also included in the preparation are browned bones and pieces of beef. Also, vegetables such as carrots, celery, and onions as well as seasonings and herbs like Bay leaves, peppers, etc are also included in the sauce.
The sauce is made by browning a roux of flour and oil and then adding the stock or water. Beef bones are then browned in an oven or over a grill as is the same with the vegetables. All these ingredients are added to the stockpot and reduced over several hours.
Tomato paste or tomato purée is also added to the mixture and further reduced. Stock may be added and reduced further to enrich the sauce.
Being a very strong and rich sauce it is never used directly as it is but is therefore used as a base for other sauces such as Sauce Africaine, Sauce Bigarade, Sauce Bourguignonne, and Sauce aux champignons. Other popular variations include Sauce charcutière, Sauce Chasseur, Sauce Chevreuil, and demi-glace among a long list of other sauces in French cuisine.