Using a standing or handheld mixer, mix butter on medium until light and creamy. About 2-3 minutes.
Turn off mixer and add powdered sugar and cocoa powder.
Mix on low until it starts to combine, about 1 minute. It might start to look crumbly, this is normal, just keep mixing.
Once the frosting has started to come together, turn speed to medium and continue mixing until fully combined.
For a lighter frosting, add 1-2 tablespoons milk or cream and continue mixer another minute.
