Use a heavy bottomed, 6-cup saucepan or your meat cooking pan with its degreased juices. Cook the onions slowly with butter and oil, or fat, for 10 to 15 minutes until they are tender and lightly browned.
Add the wine and boil it down rapidly until it has reduced to 3 to 4 tablespoons.
Add the brown sauce and simmer 10 minutes. Correct seasoning. Remove the sauce from the heat until just before serving, then continue with the recipe.
Beat the mustard mixture into the sauce. Beat in the parsley and serve.
Use a heavy bottomed, 2-quart saucepan. Cook the vegetables and ham or bacon slowly in the butter, fat or oil for 10 minutes.
Blend the flour into the vegetables and stir continually over moderately low heat for 8 to 10 minutes, until the flour slowly turns a golden, nut brown. (This is called a Roux)
Remove from the heat. With a wire whip, immediately blend in all the boiling liquid (stock) at once. Beat in the tomato paste. Add the herb bouquet.
Simmer the sauce slowly, partially covered, for 2 hours or more, skimming off fat and scum as necessary. Add more liquid if the sauce thickens too much. You should end up with about 4 cups of sauce, thick enough to coat a spoon lightly. (see cooking tip).
Taste and correct the seasoning. Strain the sauce, pressing the juice out of the vegetables. Degrease it thoroughly. The sauce is ready to use.
If you will not be using the sauce immediately then clean the sides of the pan. Float a film of stock over the top of the sauce to prevent a skin from forming. When the sauce is cold, cover and refrigerate or freeze.
Note:This recipe makes 1 quart of Brown Sauce. The sauce may be stored in the refrigerator for several days or frozen for several weeks. The longer the sauce simmers the more flavorful it will be.