Beat butter with mixer or spatula add icing sugar and mix well then add milk as much as u want and finally add the vanilla extract and mix everything well. U can add your desired color or make it rainbow.

Arrange your cakes and add the butter icing in between the cakes, plaster the cake with small amount of the icing and refrigerate the cake for 15-20 minutes. Then apply the remaining icing on the cake with spatula and decorate using nozzle and pipping bag. Add sprinkles and place butterflies the way you want. Enjoy