1 Tablespoon unsalted butter
1 Tablespoons olive oil
1 large celery root
4 cups water (or chicken stock)
Clean and slice the leeks. Peel and dice the celery root. The easiest way to peel a celery root is to use a sharp knife and carefully cut the nobby, gnarly outside peel as close and cleanly to the edge as possible.
In a large soup pot or Dutch oven, melt the butter with the olive oil over medium heat. Add the leeks and cook stirring often until wilted— about 8 minutes.
Add the celery root and cover with stock or water. If using stock, it’s okay to add water to make sure all the vegetables are covered with liquid. Add salt. How much will depend on what liquid you are using. If you are using chicken stock you may want to add 1/2-1 teaspoon depending on what type of stock you are using—salty, low sodium or homemade. If using water add 1 teaspoon of salt.
Bring to a boil, then lower the soup to a simmer. Cook until the celery root is soft— about 30 minutes.
Puree the soup with a hand blender or in a regular blender once the soup has cooled slightly. Taste and adjust salt. Blend in one more Tablespoon of olive oil to emulsify and make creamier.