Watercress Soup with Kohlrabi and Wild Garlic

Based on a Simon Hopkinson recipe that uses turnip, but as I got kohlrabi in the veg box this week, I substituted that instead. The wild garlic also arrived in the veg box and was so pungent that I had to put it outside, as it made the whole flat smell! This is just a classic watercress soup recipe with some additions: a couple of leeks, whites only (or onions if you don't have leeks) sweated in some butter, along with the whites of the wild garlic - about two stems. Add a good 250g of peeled chopped kohlrabi or turnip and allow to sweat until all is soft. Add a pint of light stock and bring to the boil, then simmer until everything is really tender, about 15 minutes. Meanwhile, wash a bunch of watercress and chop the toughest stems off. Chop them finely and add to the simmering soup. Save the leaves of the cress and garlic until last. When all is cooked, throw in the watercress leaves and finer stalks and the reserved wild garlic green leaves, bring to the boil and then immediately blend until smooth. 'Let' the soup down a little with some milk or cream, but not too much. Eat as soon as possible before that wonderful vibrant green goes.