Here's a quick, easy, and delicious cake that would be perfect for having around as an afterschool snack or for tucking into a lunchbox for a special surprise. But it's not just for kids; even adults will appreciate the combination of peanut butter and chocolate chips in the batter. The cake will keep for a few days at room temperature, wrapped well in plastic. It's great on its own, or you could drizzle it with melted chocolate for extra goodness.