?Sauce Espagnole is a classic French sauce made with a brown roux, tomatoes, and beef or veal stock. It is often used as a base for other sauces or as a flavoring for stews and braises.
Brown the onions in the hot oil; add the rest of the mirepoix and continue to brown. Add the tomato paste and cook until it begins to brown and caramelize.
Add the stock, and bring to a simmer. Whip the roux into the stock, making sure all lumps are broken up. Return to a simmer and add the sachet.
Simmer for about 1 hour, and skim the surface if necessary. Strain the sauce through cheesecloth