I'm trying to make a new brownie flavor that has a nice layer of mint cream in the middle to make a mint brownie. I've tried making the mint cream many different ways, but it keeps evaporating during the baking process. I pour half the brownie mixture into the pan, then swirl dollops of the mint cream in, then top it with the remaining batter. When the come out of the oven and I cut them the mint layer is no longer visible. I've made the mint cream by creaming butter then adding sugar and some heavy cream for consistency. I've tried creaming butter and using confection sugar with heavy cream. Any advice would be great!