Same technique I always use for squash soup: sauté a chopped shallot in some oil, add one giant celery root and two medium apples, peeled and chopped; add dry thyme, sage, and a little Hungarian hot paprika; simmer in broth until cooked through; purée. I also added a quarter-cup of low-fat sour cream I had lying around in the fridge.
The biscuits were a slightly modified version of
this recipe: I used only cheddar cheese, and I left out the cayenne pepper, which I thought wouldn't work with the soup. Oh, man, these were good -- crunchy, cheesy, and tangy.