End-of-Summer Pistou Soup

This is one of my favorite end-of-summer recipes, when the markets are bursting with the best of the summer months while welcoming the vegetables that announce the arrival of autumn. Leeks, onions, and potatoes pair up with summer squash, basil, and ripe tomatoes to create an ideal soup to enjoy at the end of the ever-shorter last days of summer. The beauty of this soup is there is no broth to prepare; the veggies create their own as you go. Feel free to add any other veggies—such as carrot