Pour your prepared brownie mix into your crock pot
In a bowl, mix together your cream cheese, egg, sugar and vanilla until smooth
Pour cream cheese mixture in strips the length of your crock pot
Take a knife to create your swirl/marble
Cover and cook on high for 3-5 hours
Take lid off briefly every 45 minutes to one and half hours to wipe off condensation, the timing depends on how quickly the condensation collects on your lid
Once your brownies are set, remove lid and let cool.