This recipe is from the New York Times. If you have more time, try roasting the carrots and leeks in the oven at 375 degrees first instead of sauteing them — the soup will develop a smokier, deeper flavor.
Clean and dice 2 leeks, discarding the tough greens.
Dice carrots to make 4 C.
Heat 2 T. butter in a heavy-bottomed pot. Add the leeks and carrots and saute for 5-10 minutes, until the leeks begin to turn color. Season generously with salt and pepper
Add 8 C. vegetable or other broth, stir to deglaze the pan, then bring to a boil. Lower to a simmer and cook until the carrots are soft. Longer cooking will allow more flavors to develop.
Remove 2 C. of liquid from the pot and reserve. Use an immersion blender or food processor to puree the soup until it is smooth, then add reserved liquid until the soup is the consistency of a thin milkshake (or however you prefer it). Reheat the soup to a simmer.
Just before serving, stir 2 T. white miso into the soup (don’t heat after adding). Serve with fresh lemon or lime wedges for squeezing.