Cut the lettuces into thin ribbons after giving them a thorough wash and discarding any tough leaves. Keep those for your tortoise. Put the lettuces in a pan with just enough stock to cover and gently simmer on a low heat, keeping a vigilant eye on them there are few things nastier than charred, acrid lettuce!
Keep simmering and adding the stock until the greens are soft. Add the peas and cook for another four minutes or so. Take off the heat, cool for a minute or two, then purée with care.
Return to the pan and, on a low heat, gently add the milk, less for a thicker soup, more for a lighter summery soup. Add the brown sugar, a pinch of nutmeg, and salt and pepper to taste.
If you are going to chill the soup, put it in the fridge, adding a teaspoon of crème fraîche to each bowl prior to serving. If eating hot, dot a tiny bit of butter on the top instead.