If using another type of nut butter, you don't need additional sugar. Let cool until room temperature and then spread over the cooled cake.
Store the frosted cake in the fridge for up to 5 days.
* If you use unrefined / extra virgin coconut oil, the frosting will probably have some coconut flavor to it. With refined coconut oil, there's no coconut taste at all.
You can't taste the olive oil once the cake is baked!
Adapted from Hershey's One Bowl Chocolate Cake.