Instructions

1. 1
   Dissolve the cold roux in a bowl by stirring in some of the cold brown stock.
2. 2
   Heat the rest of the stock in a deep, thick saucepan over a medium-high flame and bring to a boil. Lower the heat.
3. 3
   Temper the roux by ladeling some of the stock into the roux while whisking vigorously.
4. 4
   Stirring constantly, slowly pour the tempered roux into the simmering stock.
5. 5
   Dissolve the tomato paste with some of the stock and stir it into the sauce. Add the mirepoix and the bouquet garni.
6. 6
   Simmer slowly, partially covered for 2 or 3 hours. From time to time skim off any scum.
7. 7
   Add more stock if the sauce thickens too much. You should end up with a sauce that coats a spoon lightly.
8. 8
   Adjust the seasoning to taste. Strain and degrease thoroughly.
9. 9
   Refrigerate or freeze if not using immediately.