Celery Root & Green Apple Soup with Pork Sausage

I had an immense piece of celeriac, I'm guessing he was about 4 pounds...almost as big as my 5-year-old's head. This made a half-gallon of very thick pureed soup, which I thinned when serving with more chicken stock and kraut juice.

2 pounds pork sausage
2 teaspoons rubbed sage or 3-4 teaspoons minced fresh sage
1/4 teaspoon dried thyme
1 teaspoon salt
1 teaspoon white pepper
2 tablespoons (at least!) cooking fat: duck fat, schmaltz, ghee...
1 onion, peeled and chopped
1 celery root, peeled and chopped
2-3 green apples, peeled and chopped
1 quart (or more) chicken stock
salt and pepper to taste

Mix the sausage, sage, thyme, teaspoon salt, and teaspoon pepper by hand or in a mixer until the ingredients are thoroughly combine. In a heavy-bottomed stock pot, cook the meat over medium-high heat until just browned. Remove and set aside.

Add cooking fat to pan. Saute onions until soft, add celery root and apples and cook briefly. Add enough chicken stock to cover the vegetables. If you don't have enough stock, add water. Bring to simmer and cook for 20-30 minutes, until vegetables are soft. Puree soup with an immersion blender or allow to cool and puree in batches in a blender. Add pork to soup, return to simmer and cook for 15-20 minutes. Add salt and pepper to taste, keeping in mind that if you are going to add kraut juice that this will make it saltier.