Mix the chopped shallots or onion with the garlic in a pan and add the red wine. Bring to the boil then reduce until almost dry. Add the red wine vinegar and boil to reduce by three-quarters. Remove the pan from the heat.
While the shallots are still warm, add the Dijon mustard and blend in with the olive oil. Season with salt and pepper. The dressing can now be left to cool and then bo