Add powdered sugar (1 cup at a time) until smooth and creamy.
Pour this frosting over your entire cake and let it set in the fridge or freezer for 15-20 minutes.
Toss some sprinkles on top of the cake and enjoy!
Keep in mind that since you will not be lining your pan with wax paper or using oil spray, the cake will stick to the pan slightly. No need to panic! You can still EASILY cut slices with a knife and use an offset spatula to remove them from the pan and serve them in plates.
Leftovers can be stored in a sealed container in the fridge for up to 2 days.