In a frying pan, over medium heat, cook bacon until very crisp, 5-7 minutes. Using tongs transfer bacon to paper towels to drain and cool. Reserve 1 tablespoon drippings and discard the rest. Break up bacon into small bits once it has cooled and dried to crispy.
To a medium size pot, add the bacon drippings, leeks, celery root/stalks and garlic. Increase heat to medium-high and cook stirring often until crisp-tender, about 5 mins.
Add cauliflower, stock, salt and pepper – bring to boil. Cover and reduce heat to medium and simmer for about 15 mins until the cauliflower is very tender.
Pour mixture into a blender (carefully!!) or use an immersion blender. Add the half and half and blend till nice and smooth.
Return mixture to pan and cook until thoroughly warmed. Ladle soup into bowls and garnish with bacon, cheese, parsley and chives, croutons….