In a stock pot over medium heat, melt the butter and salute the leeks for 3-4 minutes.
Add the celery root, stock, and salt, bring to a boil, cover, and simmer for 18 minutes or until the celery root is fork tender.
Using a regular or immersion blender, carefully blend the soup until it is smooth and creamy.
To Freeze: Allow to cool, store in appropriate container or ziploc bag, label and freeze up to 4 months. When ready, defrost in fridge for 24 hours or place in pot and bring to heat over low-medium heat.