Transfer cake batter to a microwavable mug. Fill 3/4 or less to make room for the cake rising. Microwave the mug for 60-70 seconds. A toothpick inserted into the center should come out almost clean.
Carefully open the chilled coconut milk cans. Be careful not to shake as you want the top layer. Once open, scoop out the top layer of each can and place into the bowl.
Using the whisker, whisk the coconut cream until soft peaks form, 3-4 minutes on medium speed. Add in the powdered sugar if using and whisk until stiff peaks form. Top the cake with the whipped coconut cream.