Trim florets off broccoli head and set aside. Peel stem with a vegetable peeler to remove woody outer skin, then finely chop.

In a Dutch oven, sauté leeks, potatoes and broccoli stem with the butter until leeks are tender. Stir in garlic, savory and mustard and cook another minute.

Add broth and water and bring up to a boil. Add broccoli florets then simmer until all veggies are tender, about 15 minutes.

Stir in cheese and parsley, then puree soup using an immersion blender or food process until smooth. Return to pot and stir in sour cream and season to taste with salt and pepper.