I've been making whoopie pies for as long as I can remember but have yet to figure out why they sometimes puff into lovely half moon shapes and other times, they're nearly as flat as pancakes. I prefer the esthetics of the puffy pie and just wondered if anyone has a clue. Thought refrigerating the batter would reduce spreading and flattening but I haven't found that to be the case. Is it a function of mixing the batter until just blended as with some other baked goods? Any other ideas? Thanks.