Firstly make the base for the sauce. Place all of the ingredients apart from the vinegar, tomatoes and basil into a small pan and put onto a gentle heat. Warm the sauce until it is hot but not boiling and cook for about 20 minutes. The shallots should be cooked and soft but not coloured.
The sauce can now be poured into a clear jar, covered and stored in the fridge when cool. I think this sauce is better made a day or two before you intend to use it, as it allows the flavours to infuse. With correct storage it will keep for a couple of weeks.