Oprah's Favorite Kale and Farro Soup

OPRAH’S FAVORITE KALE AND FARRO SOUP1 T. olive oil1 small yellow onion finely chopped1 leek, white and light green parts only, halved and rinsed and thinly sliced2 medium carrots, diced2 celery stalks, diced2 c. pearled farro, rinsed and drained1 lb…