Line a sheet pan with parchment paper and spread out popcorn on top.
Chop white bark so that there are no pieces bigger than 1 ounce. Place in a microwave safe bowl. Microwave on high for 30 seconds. Stir. Continue microwaving for 20 second intervals, stirring in between until completely melted.
Stir cake batter into melted white bark and add sprinkles.
Using a spoon, drizzle melted white bark on top of popcorn. It will probably be too thick to drizzle, so just glop it out. Use a spatula or your hands (easiest way) to evenly coat the popcorn in the white bark mixture.
Sprinkle with nonpareils.
Let it set up for a few minutes before eating. Best eaten soon after it is made.