Line a square dish with parchment paper and coat with non-stick cooking spray.
In a large pan over medium high heat melt butter. Spread over the entire bottom of the pan.
Sprinkle white chips in an even layer over the butter. Pour sweetened condensed milk evenly over chips. After a couple minutes of allowing chips to warm up stir the mixture often until chips are melted.
Turn heat to medium low and add vanilla and stir well.
Add the cake mix and stir well.
Then add sprinkles and stir well. Remove from heat.
Pour into lined baking dish and tap gently on a firm flat surface until mixture is level.
Chill for at least 1 hour and then cut into squares. Keep chilled until ready to dip in chocolate.
Melt candy coating chocolate and dip squares. Shake excess chocolate off and decorate with sprinkles immediately. Enjoy!