1. Put the chocolate chips and peanut butter chips in separate, heat-safe bowls. Mix together the marshmallow, milk, butter and sugar over medium heat. Bring mixture to a boil, stirring constantly. Boil and stir for five minutes. Remove from heat and stir in vanilla. Pour half the mixture into each bowl of chips; stir until melted.
2. Pour melted chocolate into foil-lined 8 by 8 inch pan.
3. Quickly pour the melted peanut butter chips over it. Let cool on the counter.