I should say that I first had the idea when making a syrup with lemon balm for some jelly. If you've got a garden, this is easy to come by, but if you haven't there is no way you can buy it. I tried, then, substituting lemongrass, weight for weight, and it worked beautifully. By the same token, if you have got verbena in the garden then do use that here.
Recipe posted by Nigella