Cook bacon in a large, heavy pot over medium-high heat until crisp. Remove from pot and reserve.
Add the leeks to the pot and sauté, stirring occasionally, over medium-high heat until softened, 4-5 minutes.
Add the cauliflower, chicken stock, and cayenne. Bring to a boil then reduce heat, cover, and simmer for 20 minutes or until cauliflower is very tender.
Puree the soup in batches in a blender or food processor or with an immersion blender.
Stir in the Parmesan, Greek yogurt, and salt to taste. (I start with a 1/2 teaspoon of Kosher salt, then check and add another 1/2 teaspoon typically. Amount will depend on individual taste and the type of broth or stock you use.)
Ladle into bowls and sprinkle with reserved bacon and extra Parmesan cheese.
