Watercress and potato soup, from the March chapter of Elisabeth Luard's A Cook's Year in a Welsh Farmhouse. The recipe given is actually for sorrel and potato with the suggestion to substitute watercress if you have no sorrel to hand. It turned out velvety and peppery, and with that chlorophyll-rich vivid green (the picture above was taken before the addition of some double cream or crème fraîche, the one below after) it looked and tasted wonderful.
The book is illustrated with great photographs by Clare Richardson but also with Elisabeth's own watercolours, some of which you can see here, so leafing through it is as much a pleasure as cooking from it.