Hi, Susan. did the frozen butter go in first, to the hot meringue, or later on, once the frosting was underway? If the latter, you may never get the frosting to be totally smooth without pressing it through a strainer and getting any unemulsified butter bits out of it. You could also let it sit overnight at room temperature (allowing any hard butter bits to temper) and whip again tomorrow; it's certainly worth a try. Susan

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