Combine 7 cups chicken broth, potatoes and garlic cloves in large pot. Bring to boil. Reduce heat to medium; cover and simmer until potatoes are very tender, about 25 minutes. Working in batches, puree soup in blender until smooth. Return to same pot. Add half and half and bring to simmer. Thin with more broth if soup is too thick. Season to taste with salt and pepper. Stir in chives. (Can be prepared 1 day ahead. Cover and refrigerate. Rewarm over low heat, stirring frequently.) Ladle soup into bowls. Top with dollop of sour cream and serve.