The secret ingredient here? it’s a spoonful of actual cake mix. All you must do is whisk it well into the melted white chocolate. Best decision ever. And don’t worry about “what to do with the rest of the cake mix.” Store it for later. Make more bark. Make cake-mix cookies. Eat it off a spoon. Bake a cake.
Melt dark chocolate either in the microwave or a double boiler. Line a baking sheet with parchment paper and pour chocolate on. You can smooth it with a spatula to the thickness you desire. Stick in the freezer for 20 minutes.
Melt white chocolate. Whisk in cake mix slowly, stirring well until no lumps remain. Let it set for 3 full minutes (or at least until it slightly thickens).
Remove baking sheet with chocolate from the freezer and immediately pour white chocolate on top. Sprinkle on sprinkles. Freeze for 20 minutes.