In a microwave-safe bowl, combine the butter, cocoa powder, and sugar and microwave on full power for 30 seconds. Stir and return the bowl to the microwave for another 30 seconds. Stir again. If the butter isn’t mostly melted, microwave it for another 15 to 30 seconds. Let the mixture cool for 1 minute.☞ TESTER TIP: You can instead melt the butter, cocoa powder, and sugar mixture, in a medium saucepan over low heat and remove it from the heat to cool slightly.