1 In A Large Pot, Heat The Butter Until Frothy, Then Cook The Onions Over Medium Heat Until Soft And Translucent, About 5 Minutes. Salt The Onions As They Cook. Add The Wine Or Stock, Potatoes And Water And Bring To A Boil. Turn The Heat Down To Low, Cover The Pot And Simmer Until The Potatoes Are Soft, About 30 Minutes. 2 Add The Watercress To The Pot. Stir Well And Cook For 2 Minutes. Turn Off The Heat And Pur