Bring chicken stock, diced potatoes and garlic cloves to boil in heavy large saucepan. Reduce heat to medium and cook until potatoes and garlic are tender, stirring occasionally, about 15 minutes. Puree mixture in batches in blender or processor. Return puree to saucepan. Stir in milk. Season soup to taste with salt and pepper. (Can be made 1 day ahead. Cover and refrigerate.) Mix butter and rosemary in small bowl to blend. Bring soup to simmer. Ladle soup into bowls. Top each with small spoonful of rosemary butter. soup 24