Prepare the cake according to package instructions. Let cool completely before moving on to the next step.

Using a fork or your hands, break the cake into fine crumbs into a large bowl. Add softened cream cheese and knead gently with your hands until cream cheese is fully incorporated.

Roll into 42 cake balls (about 1 heaping tablespoon per ball) and place on a wax paper-lined baking sheet. Place in the fridge to chill while you prepare the chocolate.

Heat chocolate in a heatproof bowl until completely melted. Add oil, if using, and stir to combine. Remove cake balls from the fridge and place one ball at a time into the melted chocolate. Using a fork, evenly coat each ball with the chocolate. Use the fork to remove the truffle from the chocolate and before transferring it back to the baking sheet, slightly tap the fork against the side of the bowl to get rid of any excess chocolate. Place on the baking sheet and repeat with remaining cake balls.

Pour leftover melted chocolate into a small ziptop bag, cut off one corner and pipe melted chocolate in desired design on top.

Return truffles to the fridge for 15 minutes or until truffles are set.