Avocado and Potato Salad with Fresh Herbs

3kg desirée, potatoes, peeled and cut into 3 cm pieces 1/3 cup flat-leaf parsley leaves 2 tbsp finely chopped chives 1 tbsp chopped tarragon 3 ripe avocados, peeled and sliced   DRESSING ¾ cup extra virgin olive oil Finely grated rind of 1 lemon ½ cup lemon juice   For dressing combine all ingredients, season to taste and mix well. Cover potatoes with water in a saucepan, bring to the boil and boil for about 7 minutes, or until just tender.  Drain.  Transfer potatoes to a bowl and, while still warm, pour dressing over and toss gently.  Just before serving, add herbs and avocado to salad and toss gently to combine.