This ooey gooey Slime Cake is as delicious as it is fun!
In the bowl of an electric stand mixer fitted with whisk attachment, whisk butter and sugar on medium high speed until very pale and fluffy or about five minutes.
Once all cream has been added and mixture is mostly combined, turn off the mixer and scrape down the sides of the bowl.
Now turn the mixer onto medium-high to high and whisk for 3-5 minutes or until mixture is lighter and fluffier. (Keep an eye on the buttercream. You may want to add another teaspoon of black food color to reach the desired depth of color.)
The frosting will be shiny and seem to have many large air bubbles throughout and this is exactly what we are going for. (You can smooth those out on the cake if so desired.)