Over moderate heat, melt butter ... balloon whisk until soup becomes a little smoother. Season ... add a little buttermilk or more broth as soup thickens as it stands.
Melt butter in large saucepan ... 5 minutes). Add potato slices and broth; bring to ... balloon whisk until soup becomes a little smoother, but ... add a little buttermilk or extra chicken broth because ... six 1 cup servings.