1Line an 8-inch-square baking pan with wax paper or foil, and coat with non-stick spray.
2In a microwave-safe bowl, combine the dark chocolate chips, heavy cream and half of the sweetened condensed milk. Microwave the dark chocolate mixture in 20-second intervals, stirring in between each interval, until the chocolate is melted.
3Add the vanilla extract to the dark chocolate mixture and stir well until smooth.
4Transfer the dark chocolate mixture into the prepared pan and spread into an even layer.
5In a separate bowl, combine the white chocolate chips with the remaining half of the sweetened condensed milk. Microwave the white chocolate mixture in 20-second intervals, stirring in between each interval, until the chocolate is melted.
6Evenly spread the white chocolate mixture on top of dark chocolate layer.
7Top the chocolate layers with the Mallow Bits or miniature marshmallows, and gently press them down.
8Refrigerate for 4 hours, or until set.
9Remove the fudge and wax paper from the pan. Carefully peel all of the wax paper from the fudge.
