Preparation

• Heat the oven to 375ºF. Scrub the potatoes in water, pat dry, and pierce in several places with a fork. Set them directly on an oven rack and bake until very tender when pierced with a fork, about 1 hour. Let cool completely on a wire rack.
• Melt the butter in a soup pot over medium-low heat. Add the leeks and garlic, season with salt, and cook, stirring occasionally, until softened, about 10 minutes. Add the broth and 2 cups water. Bring to a simmer over medium heat and cook until the leeks are very tender, about 20 minutes.
• Meanwhile, put the bacon in a skillet and cook over medium heat, stirring occasionally, until browned and crisp, 8 to 10 minutes. Transfer the bacon bits with a slotted spoon to a saucer lined with paper towels to drain and cool.
• When the potatoes are cool, cut one of them in half lengthwise. Use a large spoon to scoop the flesh in one piece from each half. Cut the flesh into 1/2-inch cubes and set aside. Coarsely chop the potato skin and the entire remaining potato and add to the pot with the leeks. Purée the contents of the pot in a blender until very smooth (you’ll need to work in two batches). Return the puréed soup to a clean soup pot and reheat over medium low. Whisk together the milk and sour cream until smooth and then whisk this into the soup, along with 1/2 cup of the Cheddar. Stir in the diced potato. The soup should be fairly thick, but if it seems too thick, thin it with a little water. Season to taste with salt and pepper. Serve garnished with the remaining Cheddar, the bacon bits, and the scallions or chives.