Melt chocolate in short bursts in the microwave until completely melted. (epicurious.com)
Make the chocolate Italian meringue buttercream: melt chocolate in short bursts in the microwave until 2/3 melted; stir until completely melted and set aside to cool slightly. (lapechefraiche.com)
I would be a little careful and warm it up in short bursts in the microwave because of the egg. (lowcarbmaven.com)