This is a classical French brown sauce, also called sauce espagnole. It is the basis for many other sauces. The secret is to use good quality, strong beef stock and to simmer the sauce very slowly. It freezes well.

1/2 cup diced carrots
1/2 cup diced onion
1/2 cup diced celery
4 tablespoons diced lean bacon, blanched and drained
4 tablespoons clarified butter
4 tablespoons flour
8 cups beef stock, boiling
3 tablespoons tomato paste
4 large sprigs parsley
1 bay leaf
1/2 teaspoon thyme
Salt, to taste
Freshly-ground pepper, to taste

In a heavy 2-quart saucepan, saut?vegetables and bacon in the butter until soft. Slowly blend in flour and stir constantly over medium heat for approximately 10 minutes or until the flour is golden brown. Remove from the heat and add the beef stock all at once, stirring constantly. Stir in tomato paste and add herbs. Simmer very slowly, partly covered, for at least 2 hours. The longer the sauce is simmered the better it will be. Stir occasionally and skim off any fat or scum from the top. When the sauce is the consistency of heavy cream, correct the seasoning and strain through a fine sieve.