Winter Vegetable Soup with Watercress Pistou

1. 1
   Heat the oil in a medium saucepan over medium heat until shimmering. Add the onion, season with salt and pepper, and cook, stirring occasionally, until softened and just beginning to turn golden brown, about 5 minutes. Add the mustard, stir to coat the onion, and cook until fragrant, about 1 minute.
2. 2
   Add the remaining ingredients, season generously with salt and pepper, and stir to combine. Bring to a boil, then reduce the heat to medium low, cover, and simmer until the vegetables are tender, about 15 minutes.

For the pistou:

1. 1
   Meanwhile, combine the watercress, garlic, and Parmesan in a blender. Remove the small cap from the blender top, cover the hole with a kitchen towel, and turn the blender on. Remove the towel and add the oil in a slow, steady stream until evenly incorporated. Stop and scrape down the sides of the blender, then pulse until smooth. Taste and season with salt and pepper as needed.

To serve:

1. 1
   Remove the soup from the heat and discard the bay leaves. Taste and season with additional salt and pepper as needed. Ladle the soup into serving bowls and top each bowl with a heaping teaspoon of the pistou.