Heat chicken broth, cream and butter just to boiling in medium-sized saucepan; remove from heat. Gradually stir in potato granules and chives. Whip briskly with fork or whisk until fluffy, about 1 minute. Stir in sour cream and sherry. Spoon into buttered 1-quart casserole and bake at 350 degrees F for 15 minutes, or until piping hot.