Place marshmallows on cookie sheet lined with parchment paper. Place on lower rack of oven, and broil marshmallows until nice and brown. Be sure to keep an eye on them?hey burn very, very quickly. Combine butter and icing sugar in electric mixer fitted with paddle attachment, on low until blended (about 1 minute). Add vanilla and mix on high for about 3 minutes. Add marshmallow cream and toasted marshmallows, and mix on lowest setting for about 1 minute.