Yes, absolutely! If you carry on simmering the soup beyond 20 minutes, your potatoes will start to break down by themselves. You can just lightly stir it and you will have a partly blended soup with chunky leeks. If you wanted to make the soup even more creamy, you could boil the potatoes separately, mash them and then add them to the rest of the soup. This is also a great way to use up potatoes from last night dinner.