Procedure We want to saute the mirepoix in the fat until it is well caramelized.Add the flour with the mirepoix to create a roux and cook until you create a brown roux.Add the tomato puree, stir in to remove any lumps of roux. Add brown stock and bring to a boil, then reduce to a simmer.Simmer for about 1-1.5 hours, allowing the sauce to reduce. Skim the surface to remove the scum and impurities.Strain the sauce with a conical strainer and several layers of cheesecloth. Cool in a water bath.MirepoixA mirepoix is a flavor base made from diced vegetables cooked—usually with butter, oil, or other fat—for a long time on low heat without coloring or browning.
