Put the duck legs on a baking tray, sprinkle with sea salt and black pepper, then put in the oven. Immediately turn the heat down to 180ºC/gas 4 and cook for about 35 minutes, or until the skin is crispy and the meat is moist and tender. Leave to rest for 5 minutes.
Destone and place the cherries in a salad bowl with the watercress. Crumble in the feta.
Make the vinaigrette by mixing together the ingredients in a jar or glass.
Shred the duck meat, add it to the bowl, pour over the vinaigrette, toss and serve.
If you don't have plum seed oil, use an extra teaspoon of extra virgin olive oil, plus a few drops of almond essence.