Heat 6 tablespoons of the butter in a large soup pot over medium heat. Add the onion, leeks, and garlic and cook,covered, stirring occasionally, until soft.
Raise the heat to high, pour in the vermouth, and cook, uncovered, until almost dry, about 4 minutes.
Add the potatoes, water, and salt. Toss in the parsley, thyme, and bay leaf. Bring to a boil, lower the heat, and simmer, covered, until the potatoes are tender, about 20 minutes. Remove from the heat and allow to cool.
If you have a regular blender, wait till the potato mixture has cooled. Then, working in batches, transfer the mixture to a blender and puree until smooth, or puree with an immersion blender. If you have a high end blender with a large canister, you may be able to put all of it in at once. Just be sure to leave enough room for expansion. If you put the hot liquid in and turn a blender on it may blow the top off and you will have no soup and a big mess to clean up!
Return soup to the pot and re-heat over medium heat if needed. Whisk in the rest of the butter (2 tablespoons) and heavy cream.
Season to taste with sat and pepper.
Garnish with chives if you want, and serve immediately.