Line an 8-inch square pan with foil (leaving a good overhang on all sides), and spray lightly with nonstick spray.
Prepare the chocolate fudge layer: In a medium sized saucepan, combine the chocolate chips, sweetened condensed milk and marshmallow creme and heat over medium heat. Stir constantly with a rubber spatula or wooden spoon as the chips melt. Once the mixture is melted and smooth, remove from heat and scrape into the prepared pan- spreading to create an even layer. Set aside.
Prepare the white fudge layer: In a medium sized saucepan, combine the white chocolate chips, sweetened condensed milk and marshmallow creme and heat over medium heat. Stir constantly with a rubber spatula or wooden spoon as the chips melt. Once the mixture is melted and smooth, remove from heat and stir in the vanilla. Then quickly stir in the 1/3 cup sprinkles. Don't stir too much or they will begin to melt into the mixture. Scrape the mixture on top of the fudge layer- spreading to create an even layer. Sprinkle a few additional sprinkle or nonpareils on top, if desired.
Refrigerate for 4 hours, or until set. Once set, remove the fudge from the pan by lifting it out of the pan with the foil overhang and then peeling the foil off and discarding. Set the fudge on a cutting board and cut into small pieces. Store at room temperature for up to 3 days, or freeze in a well-sealed container until ready to munch.