Preheat your oven to 350°F (175°C). Spread the cake mix on a baking pan and bake for 3-5 minutes. Let it cool completely before adding to the frosting.
In a large bowl, using a standing mixer or handheld mixer, beat the softened butter on medium-high speed for 3-5 minutes until it becomes very light and fluffy.
Gradually add the cooled cake mix and powdered sugar. Mix on low speed until the ingredients start to incorporate and become crumbly, about 30-60 seconds.
Once the mixture begins to come together, increase the speed to medium-high and continue beating for another 3-5 minutes until the frosting is smooth and fluffy.
If the frosting is too thick, add 1-2 tablespoons of milk or cream to thin it out, continuing to mix until the desired consistency is reached.
If desired, add sprinkles or food coloring, and mix for an additional 15-30 seconds to evenly distribute.