Allow to cool until it has thickened but is still pourable, about 10 minutes. Don’t place ganache in the fridge to cool. Test the consistency of the drip by pouring down the side of a glass. If it’s too thick, microwave for 5 to 10 seconds. If it’s too thin, allow to continue to cool. Spread the drip all over the top of the cake and allow it to drip down the sides.
Allow to set slightly before garnishing with the peanut butter cups, if using.
Brownie cake adapted from Cloudy Kitchen.