In a large saucepan over medium heat, add bacon and fry until crispy. Remove and set aside.
Continue on medium heat, add olive oil to pan, stir in leeks, and onions, sauté for about 5 minutes, until the start to soften. Stir in celery, potatoes and cauliflower to coat. Add stock and salt, bring to boil, then reduce heat and simmer until the vegetables are tender. Remove from heat.
Using a hand immersion or blender, puree the soup until smooth and no chunks remain. Return to heat, adjust seasoning if necessary. In a small bowl, add the sour cream and add a couple of ladles of the soup and mix well with a fork or whisk. Pour the sour cream mixture into the hot puree soup, and whisk until well blended.
Ladle into bowls and garnish with chopped chives, parsley, and bacon. Serve with crusty bread.
