Add all ingredients except the chocolate chips (if using) to an 8-ounce or larger microwave-safe mug. Use a fork to stir together until combined. It might seem lumpy at first but keep stirring and it’ll resemble cake batter in no time!
Microwave on high until the cake has risen and springs back slightly when you poke it, 45-60 seconds. If it’s not done after 60 seconds, try cooking in 15-second intervals until done.
Top with chocolate chips or chunks if desired and enjoy right away.