In a 6-quart stockpot on high heat, add the olive oil, rutabaga, turnips, and leeks. Saute for 2 minutes. Add the stock and bring to a boil, then simmer for 20 minutes. Add the baby spinach, watercress, and baby spinach, bringing the soup to a boil again, cooking for 5 minutes. Adjust seasoning if necessary. To serve, ladle in a soup bowl and enjoy the healing properties of this earthy and medicinal soup.