Trim the leeks and discard the very dark parts.
Slice them length-wise. With each half of leek, fan it out and thoroughly wash, removing dirt between the leaves. Slice and place in a colander. Rinse again and set aside. Drain. Shake before adding the leeks to the soup.
Turn the Instant Pot on Sauté mode. Add the butter, onions, shallots, and leeks. Cook until the leeks start to soften. Watch carefully and stir often. You do not want the vegetables to get brown. The volume should reduce to almost half.
Once the leeks are soft, add the potatoes, garlic, thyme, rosemary, coriander, salt, pepper, nutritional yeast, and vegetable broth
Set to high-pressure cooker mode and cook for 10 minutes. Release the pressure and unplug.
Remove the thyme and rosemary sprigs.
Using an immersion blender, puree just until smooth.
Stir in the milk and the cream.
Refrigerate for several hours to chill. Thin with more milk if necessary.
Ladle the soup into small bowls, garnish as desired and serve.
If you do not want to use an Instant Pot, this soup can be made on a stove top. The directions are the same. After the soup comes to a boil, turn to low and simmer until the potatoes are soft. Remove the soup from the burner and blend.
You can use any plant-based creamer and milk that you wish. We used So Delicious Coconut Creamer and So Delicious Coconut Milk (beverage).
This is a very rich soup and is meant to be served in small bowls or glasses for sipping. To lower the fat content, omit the butter and the sautéing step. Simply add the onions, shallots, and leeks to the pot with the other ingredients and cook. You can also eliminate the cream and only use milk.