Brown the meat pieces (if using off the shelf stock, including the beef or veal trimming) in a little oil on a moderate heat for a few minutes.
Discard the meat pieces and pour off the excess fat.
Reduce the heat, add the butter and then the carrots, celery, onions and thyme (and mushrooms if used) and cook for 1 or 2 minutes.
Stir in the flour. Toasted flour can be used to avoid the need of cooking the flour but if you're using untoasted flour, cook the roux on low heat for a few minutes.
Add the tomato paste and mix and cook for about a minute.
Add the stock and the white wine and bring to the boil and reduce on low heat for 15 – 20 minutes.
Place shallots, wine and vinegar in a pan and on high heat reduce to about ½ the volume.
Add 300 ml (10.55 fl oz) of the sauce base to the pan and bring to the boil.
Reduce heat to low and simmer for 10 minutes, and then season to taste with salt and pepper.
With the heat off, add the herbs and gherkins and whisk together.
Allow the herbs to infuse after which the sauce is ready to use.
