and just enough cold water to cover the potatoes. bring the water to a boil and cook until the potatoes are tender about 10 minutes or until you can place a knife through the potatoes without resistance.
drain the potatoes and return them to the pot. add the remaining 1/2 teaspoon salt and the olive oil and then mash with a potatoes masher or the back of a fork.
stir in the ground pepper and chives. fold in the watercress. if they seem a little dry you can add a little chicken stock but only add a tablespoon at a time. makes bout 4-5 cups. 