Celery plays a big role in the flavor of this creamy soup. For a vegan soup, you can substitute coconut oil for the butter. Non-vegans can add some cream or yogurt before serving to make it extra creamy.
Optional: Trim the leafy stems off the top of 1 head of celery, then rinse them and throw in a pot with 8 cups of water. Add a sprig or two of any fresh herbs you have. Bring to a boil and then simmer for at least 2 hours or overnight.
Clean and trim spring onions and then chop white and green parts to make 2 C.
Clean and trim 8 stems of celery and cut into small dice.
Heat 2 T. olive oil and 1 T. butter in a heavy bottomed pot, then add the onions (white parts only) and celery. Saute for 10 minutes or until the onions begin to brown.
Meanwhile, trim the stems off 1 head of cauliflower. Cut the head in half top to bottom, then finely chop the entire head including the core. Add to the pot along with 1/2 t. salt and a generous amount of black pepper. Saute for 8-10 minutes.
Add 6 C. of your homemade vegetable broth, or storebought vegetable or chicken broth. Bring to a boil, then simmer.
Dice 3-4 medium potatoes to make 2 C. and add to the soup. Simmer for 20 minutes.
Puree the soup in batches, then add the chopped onion greens and allow to simmer another 5 minutes. Taste and add more salt and pepper as necessary.