Place cake batter in muffin tins, filling 1/3 full to make very small muffins. I do this to make the whoopie pie shape instead of pouring small amount of cake batter on to parchment paper on a cookie sheet. The olive oil sometimes makes the batter runnier so that the pies spread out too much. Using the muffin pan is an easy way to make uniform shaped Whoopie pies.