Stir chopped chocolate and butter in a large bowl set over same saucepan of simmering water until melted and smooth, 4 - 5 minutes; set aside. (epicurious.com)
Place the bowl over a small pot of simmering water, making sure the bowl doesn't touch the water. (glutenfreeonashoestring.com)
Melt the chocolate and butter in a bowl set over a pan of simmering water until smooth and all of the chocolate is melted. (guittard.com)