Pop each bag of popcorn as you normally would in the microwave.
In a microwave-safe bowl, add 6 ounces of the white candy bark/white chocolate and place in the microwave for 30 seconds. Remove, stir, and repeat for another 30 seconds. Stir, and if you need to add it to the microwave one more time, just try it for about 20 seconds. It'll likely be fully melted after the 2nd round in the microwave, though! Set aside once it's melted.
Shake the first bag of popcorn up and down for a few seconds to get the unpopped kernels to fall to the bottom of the bag.
Using your hand, scoop out about 1/3-1/2 of the popped popcorn into a large bowl. (Don't pour it in so you can avoid the unpopped kernels!) Add part of the melted baking bark to the popcorn, lightly stir, and repeat with remaining popcorn in the bag & melted baking bark.
Pour popcorn mixture on large baking sheet covered with foil. Immediately add sprinkles (and other toppings) so that it sticks to the melted baking bark.
Repeat steps 1-5 with other 2 bags of popcorn & remaining baking bark.
Allow the popcorn set: it'll take about 30 minutes-1 hour for the melted baking bark to harden at room temperature. Or, you can just put the pan in the fridge for a few minutes and it won't take but 5-10 minutes to completely set!
Gently lift the foil on either end to help break up the popcorn and then use it as a funnel to put all of the popcorn in a large bowl, or break apart and add to goodie bags or mason jars for gift-giving. ENJOY!