Bust out the wands, it's time for some kitchen magic. Line an 8"-x-8" pan with aluminum foil and spray with cooking spray. We'll need that later.

Let's make the butterscotch layer: In a medium-sized saucepan over medium-low heat, melt butter, then add the condensed milk and butterscotch chips. Stir the pan until all of the chips have melted and the mixture has fully combined. Pour into that sprayed pan you prepared.

Now for the white chocolate swirl: In another small saucepan over medium-low heat, combine condensed milk, vanilla, and white chocolate chips and stir until chips have melted. Same basic deal. Remove the pan from the heat and drizzle the white chocolate mixture on top of the butterscotch fudge, then use a butter knife to gently swirl the two flavors together. Top with marshmallow bits, if desired (and really, why wouldn't they be), using your hands to press them into the top of the fudge.

Now just refrigerate for at least 4 hours. When it's set, cut into slices and serve. Now if I could just figure out where my Chocolate Frog went...